See below.
Step-by-step explanation:
To find the surface area, find the area of the square base and add it to the area of each triangle face. Find the area of the base by multiplying base length by base length. Find the area of each triangle face by multiplying 1/2 * b*h.
Example:
For a base which is 12 by 12. The area is 12 x 12 = 144.
For the triangle face, the area is 1/2 * 12 * 15 = 90. Since there are 4 faces, the total area is 4 * 90 = 360.
Together the surface area is 360 + 144 = 504.