If you're describing a time, then it has to have a unit of time. We have no idea how much gas you're talking about, so second, minute, and hour are all possibilities.
36 + x would be your answer. When something is 'increased', you are adding to it. Such as saying 47 increased by -5x is the same as 47 + (-5x). If this wasn't the answer you were looking for, let me know. For now, I hope this helped:)
