#include <bits/stdc++.h>
using namespace std;
using ch = char;
using ll = long long;
using ld = long double;
using db = double;
using st = string;
using vdb = vector<db>;
using vvdb = vector<vdb>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vd = vector<ld>;
using vvd = vector<vd>;
using vs = vector<st>;
using vvs = vector<vs>;
using vc = vector<ch>;
using vvc = vector<vc>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
const ll mod = 998244353;
const ll MOD = 1000000007;
const ll INF = 1000000000000000000LL;
using pall = pair<ll,ll>;
using vp = vector<pall>;

int main(){
    ll T;
    cin>>T;
    while(T--){
        ll L,R,A,B;
        cin>>L>>R>>A>>B;
        cout<<max(A*L+B,A*R+B)<<endl;
    }
}