J=lambda:map(int,input().split())
T,*_=J()
for _ in[0]*T:
	N,M=J();m,s=10**9,1
	for p in[2,5]:
		while m%p<1:
			if N%p:break
			elif M%p:s=0;break
			else:N//=p;M//=p;m//=p
	n=-pow(N,-1,m)*M%m if s else-1
	print([n,m][n<1and s])