for _ in range(int(input())):
    x, y = map(int, input().split())
    a, b = map(int, input().split())
    b = min(b, a + a)
    if x < y:
        x, y= y, x
    print(y * b + (x - y) * a)

fun main() {
    val T = readLine()!!.toInt()
    for (tc in 1..T) {
        val t = readLine()!!

        val s = t.toCharArray().distinct().joinToString("").repeat(t.length)
        println(s)
    }
}

#include<bits/stdc++.h>

using namespace std;

const int N = 40043;

int len;
int p[N];

void build(int a, int b)
{
	len = a * b;
	p[0] = 0;
	for(int i = 1; i <= len; i++)
	{
		p[i] = p[i - 1];
		if((i % a) % b != (i % b) % a)
			p[i]++;
	}
}

long long query(long long l)
{
	long long cnt = l / len;
	int rem = l % len;
	return p[len] * 1ll * cnt + p[rem]; 
}

long long query(long long l, long long r)
{
	return query(r) - query(l - 1);
}

int main()
{
	int t;
	cin >> t;
	for(int i = 0; i < t; i++)
	{
		int a, b, q;
		cin >> a >> b >> q;
		build(a, b);
		long long l, r;
		for(int j = 0; j < q; j++)
		{
			cin >> l >> r;
			cout << query(l, r) << " ";
		}
		cout << endl;
	}
}

#include <bits/stdc++.h>

#define forn(i, n) for (int i = 0; i < int(n); i++)

using namespace std;


int main() {
	int n, k;
	scanf("%d%d", &n, &k);
	vector<int> a(n);
	forn(i, n) scanf("%d", &a[i]);
	vector<int> c(k + 1);
	forn(i, k) scanf("%d", &c[i + 1]);
	
	sort(a.begin(), a.end(), greater<int>());
	int ans = 0;
	for (int i = k, g = 0; i >= 1; --i){
		while (g < n && a[g] == i) ++g;
		ans = max(ans, (g + c[i] - 1) / c[i]);
	}
	vector<vector<int>> res(ans);
	forn(i, n) res[i % ans].push_back(a[i]);
	
	printf("%d\n", ans);
	forn(i, ans){
		printf("%d", int(res[i].size()));
		for (auto it : res[i])
			printf(" %d", it);
		puts("");
	}
	return 0;
}

#include<bits/stdc++.h>

using namespace std;

const int MOD = 998244353;
const int N = 200043;

int add(int x, int y)
{
	return (x + y) % MOD;
}

int sub(int x, int y)
{
	return add(x, MOD - y);
}

int mul(int x, int y)
{
	return (x * 1ll * y) % MOD;
}

int binpow(int x, int y)
{
	int z = 1;
	while(y > 0)
	{
		if(y % 2 == 1)
			z = mul(z, x);
		x = mul(x, x);
		y /= 2;
	}
	return z;
}

int inv(int x)
{
	return binpow(x, MOD - 2);
}

int fact[N];

int C(int n, int k)
{
	return mul(fact[n], inv(mul(fact[k], fact[n - k])));
}

int main()
{
	int n, k;
	cin >> n >> k;
	
	if(k > n - 1)
	{
		cout << 0 << endl;
		return 0;
	}
	
	fact[0] = 1;
	for(int i = 1; i <= n; i++)
		fact[i] = mul(i, fact[i - 1]);
	int ans = 0;
	int c = n - k;
	for(int i = c; i >= 0; i--)
		if(i % 2 == c % 2)
			ans = add(ans, mul(binpow(i, n), C(c, i)));
		else
			ans = sub(ans, mul(binpow(i, n), C(c, i)));
	ans = mul(ans, C(n, c));
	if(k > 0)
		ans = mul(ans, 2);
	cout << ans << endl;
}

#include <bits/stdc++.h>

using namespace std;

#define x first
#define y second
#define mp make_pair
#define pb push_back
#define sz(a) int((a).size())
#define forn(i, n) for (int i = 0; i < int(n); ++i)

typedef pair<int, int> pt;

const int INF = 1e9;
const int N = 15;

int n;
int a[N];
int sum[1 << N];
int dp[N + 1][1 << N][N + 1];
pt p[N + 1][1 << N][N + 1];

void solve() {
	scanf("%d", &n);
	forn(i, n) scanf("%d", &a[i]);
	
	forn(mask, 1 << n) {
		sum[mask] = 0;
		forn(i, n) if (mask & (1 << i))
			sum[mask] += a[i];
	}	
	
	forn(cnt, n + 1) forn(mask, 1 << n) forn(pos, n + 1)
		dp[cnt][mask][pos] = INF;
	
	dp[0][0][0] = 0;
	forn(cnt, n) forn(mask, 1 << n) forn(pos, n) if (dp[cnt][mask][pos] < INF) {
		int rmask = mask ^ ((1 << n) - 1);
		for (int nmask = rmask; nmask; nmask = (nmask - 1) & rmask) {
			if (sum[nmask] <= dp[cnt][mask][pos])
				continue;
			if ((nmask >> pos) == 0)
				continue;
			int npos = pos + __builtin_ctz(nmask >> pos) + 1;
			if (dp[cnt + 1][mask | nmask][npos] > sum[nmask]) {
				dp[cnt + 1][mask | nmask][npos] = sum[nmask];
				p[cnt + 1][mask | nmask][npos] = mp(mask, pos);
			}
		}
	}
	
	int acnt = 0, apos = 0;
	forn(cnt, n + 1) forn(pos, n + 1) if (dp[cnt][(1 << n) - 1][pos] < INF)
		acnt = cnt, apos = pos;
		
	vector<pt> ans;
	
	int mask = (1 << n) - 1, pos = apos;
	for (int cnt = acnt; cnt > 0; --cnt) {
		int nmask = p[cnt][mask][pos].x;
		int npos = p[cnt][mask][pos].y;
		forn(i, n) if ((nmask ^ mask) & (1 << i))
			if (i != pos - 1) ans.pb(mp(i, pos - 1));
		mask = nmask, pos = npos;
	}
	
	
	printf("%d\n", sz(ans));
	forn(i, sz(ans)) {
		int from = ans[i].x;
		forn(j, i) from -= ans[j].x < ans[i].x;
		int to = ans[i].y;
		forn(j, i) to -= ans[j].x < ans[i].y;
		printf("%d %d\n", from + 1, to + 1);
	}
}	

int main() {
	int tc;
	scanf("%d", &tc);
	forn(i, tc) solve();
		
}