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Creating an Expression from an Object

The question:

"Write an expression for the surface area of this tent. Do not include the floor."

Diagram of the tent:

Attachment 19936 (basically, a triangular prism on top of a cube.)

My work so far:

sides of the tent (cube): 4x^2

sides of the roof: (5x/8) * 2x = (10x^2/8)

front and back of the roof: x * [(5x/8)^2 - (x/2)^2]^(1/2)

= x * [ (x^2/8) ]^(1/2)

= (x^2/8)

put together: 4x^2 + (10x^2/8) + (x^2/8)

= (32x ^2/8) + (11x^2/8)

= 43x^2/8

According to the book though, the correct answer is 45x^2/8.

Where did I go wrong?