for _ in range(int(input())):
    a,b=map(int,input().split())
    if b%a==0:
        print(0)
    elif b//a==1:
        print(-1)
    else:
        T=True
        for i in reversed(range(2,b//a+1)):
            if (b-a*i)%(i-1)==0:
                print((b-a*i)//(i-1))
                T=False
                break
        if T:
            print(-1)