#include <iostream>
#include <cstdint>
#include <vector>
#include <cmath>

using namespace std;

static inline constexpr int32_t solve(const int32_t L, const int32_t R, const int32_t A, const int32_t B) noexcept
{
	if (signbit(A))
		return A * L + B;
	else
		return A * R + B;
}

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	
	uint32_t T, i;
	cin >> T;
	vector<int32_t> L(T), R(T), A(T), B(T);
	for (i = 0; i != T; ++i)
		cin >> L[i] >> R[i] >> A[i] >> B[i];

	for (i = 0; i != T; ++i)
		cout << solve(L[i], R[i], A[i], B[i]) << '\n';

	return 0;
}