#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vvi = vector<vi>;

#define f(i,a,b) for(int i = (a); i < (b); i++)
#define pb emplace_back
#define PB push_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size
#define dump(x) cout << #x << "=" << x << endl;

signed main() {

    int T;
    cin >> T;

    long long int yp, lp, ys, ls;

    for (int iii = 0; iii < T; ++iii) {
        cin >> yp >> lp >> ys >> ls;

        long long int tp = (abs(yp - lp) + yp) * ls;
        long long int tp2 = yp * ys;
        if ((ls > ys) && (yp > lp)) {
            long long int zt = (yp - lp)*ys + lp * ls;
            cout << min(min(tp, lp), zt) << endl;
        } else {
            cout << min(tp, tp2) << endl;
        }
    }

}

//2
//2 20 10 2
//10 20 10 2