Thank you for the opportunity to help you with your question!
The surface area is the surface area of the cube (less one side) 5 x 15 x 15 = 1125
To find the surface area of the triangles of the pyramid we need to find the slant height of the triangles. To do this, we use the Pythg. Thm. 7.5^2 + 9^2 = (slant-height)^2; This gives us a slant height of 11.715.
The area of the four triangles would be 4 x 0.5 x 15 x 11.715 = 351.45
Adding the two, we get a surface area of 1125 + 351.45 = 1476.45 square feet
For volume, we add the volume of the cube to the volume of the pyramid:
Cube: 15 x 15 x 15 = 3375
Pyramid: 1/3 x 15 x 15 x 9 = 675
Total volume = 4050 cubic feet
Hope this helps.
Please let me know if you need any clarification. I'm always happy to answer your questions.