#include <iostream>

int main() {
    int n;
    long long yp, lp, ys, ls;
    std::cin >> n;
    for (int i = 0; i < n; ++i) {
        std::cin >> yp >> lp >> ys >> ls;
        if (yp > lp) {
            if (ys * 2 > ls) {
                long long res = (yp-lp) * ys;
                std::cout << ((ys < ls) ? lp * ls : lp * ys) + res << std::endl;
            } else {
                std::cout << (yp - lp) * ls * 2 + lp * ls << std::endl;
            }
        }
        else {
            std::cout << ((yp * ys >= lp * ls) ? yp * ys: lp * ls) << std::endl;
        }
    }
    return 0;
}