What would the side length of the area affected if it was 216 square miles?

What is the value of x in the diagram below?

Pyramid shown has a square base that is 18 inches on each side has a surface area of 164 square inches what is the slant height

The median am of triangle ∆abc is half the length of the side towards which it is drawn, bc . prove that triangle ∆abc is a right triangle, and find angle mac and abm