Please help me understand this!

Okay first let’s find the middle rectangle part. so 15x12= 180. yay. for the triangles we can solve base * height and divide it by two. since there’s two equal triangles we only need to solve it once and not divide since the triangles make up a square ultimately. so 12*8 =96.
now solve 180+96 and we get 276 as our answer.