2.3 Determine the percentage of total expenses which is allocated to salary​

Ibelieve the answer your looking for is d.

Well an average of 364, but possibly 252 if you are especially eager. 

Use pythagorean’s theorem and find the missing side lengths of the two smaller triangles and add them together
13^2 - 12^2 = 5
15^2 - 12^2 = 9
5+9 = 14
14 is the length of each side of the square
14^2 + 14^2 = 19.8
19.8 is the diagonal length of the inside if the square