from math import gcd
for _ in range(int(input())):
	N, M = map(int, input().split())
	N %= 10 ** 9
	M %= 10 ** 9
	if N == 0:
		if M == 0:
			print(0)
		else:
			print(-1)
	else:
		g = gcd(N, M)
		if gcd(N, 10 ** 9) > gcd(M, 10 ** 9):
			print(-1)
		else:
			print(-M * pow(N, -1, 10 ** 9) % (10 ** 9))