import Control.Applicative
import Control.Monad

main :: IO ()
main = do
  t <- readLn
  map solve <$> replicateM t f >>= mapM_ print
  where
    f = map read <$> words <$> getLine

solve :: [Int] -> Int
solve [l, r, a, b] = max (a * l + b) (a * r + b)