代码

#include <iostream>

using namespace std;

int n;

typedef long long ll;

int exgcd(int a, int b, int& x, int& y)
{
    if (!b) {
        x = 1, y = 0;
        return a;
    }
    int d = exgcd(b, a % b, y, x);
    y -= (a / b) * x;
    return d;
}

int main()
{
    cin >> n;
    while (n--) {
        int a, b, m;
        cin >> a >> b >> m;
        int x, y;
        int d = exgcd(a, m, x, y);
        if (b % d) {
            cout << "impossible" << endl;
        }
        else {
            cout << (ll)x * (b / d) % m << endl;
        }
    }
    return 0;
}