Question

How to solve #12 can't seem to figure it out after spending 20 mins on it

Answer 1

The area of one of the triangular lateral faces is

$\dfrac{401.48-166.28}6=39.2$

You're told that the slant height, which is the same as the height of the triangular face, is 9.8, so you have

$39.2=\dfrac12\times9.8\times b$

where $b$ is the length of the base of the triangle, which is also the same as the side length of the base of the pyramid. So

$b=8$