#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
void exgcd(LL a, LL b, LL &d, LL &x, LL &y) {
    if(b == 0) {d = a; x = 1; y = 0;}
    else {
        exgcd(b, a % b, d, y, x);
        y -= (a / b) * x;
    }
}int main() {
    int T; scanf("%d", &T);
    while(T--) {
        LL n, dd, x, y; scanf("%lld%lld%lld%lld", &n, &dd, &x, &y);
        LL A, B, d, X, Y, K;
        A = dd, B = n, K = y - x;
        exgcd(A, B, d, X, Y);
        if(K % d != 0) printf("Impossible\n");
        else {
            LL dx = abs(B / d), dy = abs(A / d);
            X = X * (K / d);
            X = (X % dx + dx) % dx;
            printf("%lld\n", X);
        }
    }
    return 0;
}