5x + 5
you should always add the diagrams and graphs we cannot see. this particular question is kind of borderline because we can make a graph for you.
(f + g)x = -x^2 +3x + 5 + x^2 + 2x
(f + g)x = 5x + 5
the graph of z = 5x + 5 is shown below. always use desmos when in doubt.