Is my math correct? It's about slop and proportions.

The perimeter of a movie screen is 54 meters. the screen is 18 meters wide. how tall is it?

Ireally don't understand this, i'm really an idiot but i want to know how to figure this out. !

Question 2 (essay worth 10 points) (03.02 mc) in δabc shown below, point a is at (0, 0), point b is at (x2, 0), point c is at (x1, y1), point d is at x sub 1 over 2, y sub 1 over 2, and point e is at the quantity of x sub 1 plus x sub 2 over 2, y sub 1 over 2: triangle abc is shown. point d lies on segment ac and point e lies on segment bc. a segment is drawn between points d and e. point a is at the origin. prove that segment de is parallel to segment ab.