def find_minimum_X(A, B):
    if A == B:
        return 0
    
    min_X = float('inf')
    k_start = B // A
    for k in range(k_start, 1, -1):
        if (B - k * A) % (k - 1) == 0:
            X = (B - k * A) // (k - 1)
            if X >= 0:
                min_X = min(min_X, X)
    
    return min_X if min_X != float('inf') else -1
T = int(input())
for _ in range(T):
    A, B = map(int, input().split())
    print(find_minimum_X(A, B))