#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef __int128 i128;
const int INF=0x3f3f3f3f;
const int MAX=5e5+10;
const int mod=1e9;
i128 exgcd(i128 a,i128 b,i128 &x,i128 &y)
{
	if(b==0)
	{
		x=1;
		y=0;
		return a;
	}
	i128 g,tmp;
	g=exgcd(b,a%b,x,y);
	tmp=x;
	x=y;
	y=tmp-a/b*y;
	return g;
}
i128 inv_exgcd(ll a,ll p)
{
	i128 g,x,y;
	g=exgcd(a,p,x,y);
	return g==1?(x%p+p)%p:-1;
}
int main()
{
	int T;
	ll a,b,res;
	scanf("%d",&T);
	while(T--)
	{
		scanf("%lld%lld",&a,&b);
		a%=mod;
		b%=mod;
		res=inv_exgcd(a,mod);
		if(res==-1) puts("-1");
		else
		{
			res=res*(mod-b)%mod;
			if(res==0) res+=mod;
			cout<<res<<"\n";
		}
	}
	return 0;
}