The surface area of the pyramid is 576.
The square base is 144. It's just a square, so you multiply 12 (length) and 12 ( width) , which equals 144.
Then you find the area of one of the triangles. The equation to find triangles goes like this: 0.5 x B (base: 12) x H (height: 18). That would be 6 x 18 which is 108.
Since you got the area of 1 triangle and there are 4 triangles you have to multiply 108 by 4. That'll give you 432.
SO since you have the area of all the triangles and the square base the last thing you have to do is just add it all up.
The area of the triangles plus the area of the square base = the surface area.
432 cm + 144 cm =576 cm.