#include<iostream>
#include<cstdio>
#include<cmath>
#include<vector>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<algorithm>
#include<functional>
#include<cstring>
#include<deque>
using namespace std;
int main()
{
    int sH,sM,uH,uM;
    int T;
    cin>>T;
    while(T--)
    {
        scanf("%d:%d",&sH,&sM);
        scanf("%d:%d",&uH,&uM);
        sH-=uH;
        sM-=uM;
        if(sM<0){
            sH--;
            sM+=60;
        }
        if(sH<0){
            sH+=24;
        }
        printf("%02d:%02d\n",sH,sM);
    }
    return 0;
}

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MwowNTo1MAowNTo0NAowMDowMAowMDowMQowMDowMA==

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