Why am I getting this single output wrong?

I'm new to competitive programming and I participated in Codeforce #653 in which I spent the whole time solving these problems and did not submit any code because of exceeded time limits or wrong answer for test cases. Anyway, it was awesome. I wanted to solve this problem https://codeforces.com/contest/1374/problem/A and wrote this following code.

#include <stdio.h>

int main(){
    int i,t,j,k=0;
    int x[60000],y[60000],n[60000],prev[60000];
    scanf("%d",&t);
    for(i=0; i<t; i++){
        scanf("%d %d %d",&x[i],&y[i],&n[i]);
    }

    for(i=0; i<t; i++){
    for(j=0, k=0; j<n[i]; j++ , k++){
        if(j%x[i]==y[i]){
            prev[i]=k;
        }
    }
}
    for(i=0; i<t; i++){
    printf("%d",prev[i]);
    printf("\n");
}

return 0;
}

Everything was working fine but for some test cases I'm getting different answers. This was the expected output

12339
0
15
54306
999999995
185
999999998

and my output was this,

12339
0
5
54306
999999995
185
999999998

I did not understand why I got 5 instead of 15 keeping all the other outputs correct and also could anyone please help me to optimize the code, its taking too long to compile for large inputs.