Surface Area
The square-based pyramid has a total of 5 sides. One of them is the square base and four are triangles.
The total surface area is the sum of all 5 surface areas, as follows:
At = As + 4 Atr
Where As is the area of the square and Atr is the surface area of each triangle
The area of the square base is:
As = 9 cm * 9 cm = 81 square cm
Recall the area of a square shape is the side length by itself.
Now for the area of the triangles, recall the formula is:
Atr= base * height / 2
Each triangle has a base of 9 cm and a height of 12 cm, thus:
Atr= 9 cm * 12 cm / 2 = 54 square cm
Now, the total surface area of the pyramid is:
At = As + 4 Atr = 81 + 4 * 54 = 81 + 216 = 297
At = 297 square cm