#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

int main() {
        
        int t;
        cin >> t;
        int ans;

        for(int i=0; i<t; i++){
            int l,r,a,b;
            cin >> l >> r >> a >> b;
            if(a>0){
                ans = r*a+b;
            }
            else{
                ans = l*a+b;
            }
            cout << ans << endl;
        }


}