import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
def extended_euclid(a, b):
    if b == 0:
        return (1, 0)
    else:
        xd, yd = extended_euclid(b, a % b)
        return (yd, xd - a // b * yd)

input = sys.stdin.readline
#sys.setrecursionlimit(10**9)
t = int(input())
#alist = list(map(int,input().split()))
#alist = []
#s = input()
#n,m = map(int,input().split())
#for i in range(n):
#    alist.append(list(map(int,input().split())))
for i in range(t):
    n,m = map(int,input().split())
    n %= 1000000000
    m %= 1000000000
    if n % 2 == 0 or n % 5 == 0:
        print(-1)
        continue
    x = extended_euclid(n,1000000000)[0]
    print(x*(-m) % 1000000000)