#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    unsigned long long pocet, pj, pv, rj, rv;
    std::cin >> pocet;

    for(int i = 0; i < pocet; ++i){
        std::cin >> pj;
        std::cin >> pv;
        std::cin >> rj;
        std::cin >> rv;

        if(pj <= pv) //vytah je podobmnou
        {
            if(pj * rj >= pv * rv)
                cout << (pv * rv) << "\n";
            else
                cout << (pj * rj) << "\n";
        }
        else  //vytah je nadomnou
        {
            if(rj <= rv)
            {
                cout << (pj * rj) << "\n";
            }
            else{
                unsigned long long v = pj - pv;
                double pomer = (1.0/(double)rv) / (1.0/ (double)rj);
                unsigned long long poschodiaJa = (unsigned long long)((double)v / (pomer + 1.0));
                unsigned long long poschodiaV = (unsigned long long)(pomer * ((double)v / (pomer + 1.0)));
                double aa = 0;
                if(poschodiaJa + poschodiaV  != v)  //stretli sme sa na celom poschodi
                {
                    if((poschodiaJa + 1) * rj + 2*rv*poschodiaV > poschodiaJa * rj + 2*rv*(poschodiaV+1))
                    {
                        poschodiaV++;
                    }
                    else
                        {
                        poschodiaJa++;
                        aa = (rj * (1 - ((double)v / (pomer + 1.0)-poschodiaJa)));
                    }

                }
                //cout << (2*rv*poschodiaV) +(rv*pv) << "\n";
                cout << (long long)((aa) + (2*rv * poschodiaV) +(rv*pv)) << "\n";
            }

        }
    }
    return 0;
}