思路：

分类讨论

$code$

#include<iostream>
#include<cstdio>

using namespace std;

long long t, a, b, c, n;

long long ksm(long long x, long long k)
{
	long long ans=1;
	while(k)
	{
		if(k&1)
			ans=ans*x%200907;
		x=x*x%200907;
		k>>=1;
	}
	return ans;
}

int main()
{
	scanf("%lld", &t);
	while(t--)
	{
		scanf("%lld%lld%lld%lld", &a, &b, &c, &n);
		if(c-b==b-a)
			printf("%lld\n", (a+(c-b)*(n-1)%200907)%200907);
		else
			printf("%lld\n", a*ksm(b/a, n-1)%200907);
	}
	return 0;
}