https://codeforces.com/group/nm0n1RosrQ/contest/375698/problem/K

#include <iostream>
#include<bits/stdc++.h>
#include<utility>
#define ll long long
#define ull unsigned long long
#define pi  3.14159

#define OO  2000000000
//#define ceil(w, m) (((w) / (m)) + ((w) % (m) ? 1 : 0))
using namespace std;

void yasmeen_fakhri(){
  ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
  #endif
}


void solve(){
ll a,b ;
cin>>a>>b;
double at = a/(0.08);
double bt = b/(0.1);

if (at == bt ) cout<<at<<"\n";
else {
ll af1 =at*(0.08);
ll af2 =at*(0.1);
ll bf1 =bt*(0.08);
ll bf2 =bt*(0.1);
if (af1 == af2 ) cout<<at<<"\n";
else if (bf1 == bf2 ) cout<<bt<<"\n";
else cout<<-1<<"\n";

}


}

int main() {
   yasmeen_fakhri();

int test =1;
cin>>test;
while(test--){
 solve();

}
return 0;
}