Question

http://prntscr.com/j4dyjo

Answer 1

So, we're trying to find the lateral area of the pyramid (also known as the surface area). For this, we'll need to find the area of all the pyramid's surfaces.
Now, we have 5 surfaces to work with. 4 triangles, and 1 square. Finding the area of the square should be pretty simple; length times width.
For the triangles, we'll calculate (length times height)/2, but we aren't given the height. Luckily, we can calculate this too. If you notice in the diagram, there is a right triangle drawn inside the pyramid. The hypotenuse of this inner right triangle is also the height of the surface triangles. Solving for the hypotenuse using the Pythagorean theorem, you'll be able to calculate the area of the surface triangles.