import time
import sys
#sys.setrecursionlimit(500000)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def TI(): return tuple(map(int,sys.stdin.readline().rstrip().split()))
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip())
#for i, pi in enumerate(p):
from collections import defaultdict,deque
import bisect
import itertools
dic = defaultdict(int)
d = deque()
T = I()
for _ in range(T):
  L,R,A,B = MI()
  print(max(L*A+B,R*A+B))