fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)


fun intString n =
    if 0 <= n
    then Int.toString n
    else "-" ^ Int.toString (abs n)

fun printList [] = ignore ()
  | printList (h :: tl) = 
    (
      print (intString h);
      print "\n";
      printList tl
    )


fun findMaxValue (l, r, a, b) =
    let
        fun findMaxValueAux i maxAcc =
            if r < i then maxAcc
            else findMaxValueAux (i + 1) (Int.max(a * i + b, maxAcc))
    in
        findMaxValueAux l (a * l + b)
    end


val () =
    let
        val t = readInt ()

        val cases = List.tabulate (t, fn _ => (readInt (), readInt (), readInt (), readInt ()))

        val ans = List.map (fn (l, r, a, b) =>
                               findMaxValue (l, r, a, b))
                           cases
    in
        printList ans
    end