#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for (long long i=0;i<(long long)(n);i++)
#define all(v) v.begin(),v.end()
using ll=long long;
using pll=pair<ll,ll>;
using tll=tuple<ll,ll,ll>;
const ll INF=(1ll<<60);
template<class T> void chmin(T &a,T b){
    if(a>b){
        a=b;
    }
}
template<class T> void chmax(T &a,T b){
    if(a<b){
        a=b;
    }
}
ll f(ll x,ll a,ll b){
    return a*x+b;
}
int main(){
    ll t;
    cin >> t;
    while(t--){
        ll l,r,a,b;
        cin >> l >> r >> a >> b;
        cout << max(f(l,a,b),f(r,a,b)) << endl;
    }
}