Well, you are asked to simplify this, not solve it, If the question is 17+20, you would need to find a common factor of both numbers, or solve it and place it into a simplified version which I think is wrong.
Though if the question reads out: 17+4x+5,
17+5-4x=0
22-4x
to 11-2x
I hope I did not confuse you. XD