Need to find surface area

I count three rectangles and 2 triangles.

Top rectangle 15×12

Bottom rectangle 15×13

Back rectangle 15×5

The triangles are right triangles, sides 5,12,13.  So the legs are base and height

Two Triangles     2×(1/2)×5×12

Adding it all up

A = 15×12 + 15×13 + 15×5 + 2×(1/2)×5×12

A = 15(12 + 13 + 5) + 5×12

A = 15(30) + 60 = 17(30)

A = 510

510 square feet

step-by-step explanation:

first, eliminate the parenthesis:

3

x

+

2

−

4

x

second, group like terms:

3

x

−

4

x

+

2

third, combine like terms:

(

3

−

4

)

x

+

2

→

−

1

x

+

2

→

−

x

+

2