solid geometry

The top and bottom areas are: $2 \cdot \frac{7 + 15}{2} \cdot 5 = 110$ ft²

The back side's area is 9.4 x 11 = 103.4 ft²

The front side is 5 x 11 = 55 ft²

The right side is 15 x 11 = 165 ft²

And finally the left side is 7 x 11 = 77 ft²

This means the surface area is 110 + 103.4 + 55 + 165 + 77 = 510.4 ft²

Let me know if I did anything wrong :)