import sys
from collections import deque, Counter
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 63 - 1
mod = 998244353

def solve():
    l, r, a, b = mi()
    if a >= 0:
        print(a * r + b)
    else:
        print(a * l + b)

for _ in range(ii()):
    solve()