def find_minimum_X(A, B):
    if A == B:
        return 0

    min_X = float('inf')
    difference = B - A
    def get_factors(n):
        factors = set()
        for i in range(1, int(n**0.5) + 1):
            if n % i == 0:
                factors.add(i)
                factors.add(n // i)
        return factors
    for factor in get_factors(difference):
        k = factor + 1
        if k > 1 and (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))