A = 2lw + 2lh + 2hw
A = 2(12)(3) + 2(12)(5) + 2(5)(3)
A = 72 + 120 + 30
A = 222 cm squared
Hope this helps!! :)
It is 9 because you have a 30,60,90 triangle, and then you can use pythagorean theorem.
Because a rectangular pyramid's base is square, the cross section would be as well