#include <bits/stdc++.h>

int read() {
    int x = 0, f = 1;
    char c = getchar();
    while (c < '0' || c > '9') { if (c == '-') f = -1; c = getchar(); }
    while (c >= '0' && c <= '9') { x = x * 10 + c - '0'; c = getchar(); }
    return x * f;
}

int main() {
    for (int t = read(); t; t--) {
        int l = read(), r = read(), a = read(), b = read();
        std::cout << std::max(a * l + b, a * r + b) << "\n";
    }
    return 0;
}