Answer:
(a) 
Step-by-step explanation:
The question is incomplete. (See comment for complete question).
From the completed question, we have:

--- number of pyramids
Required
An expression for the area of the base
The total base length of the pyramid represents the perimeter of the base.
And since the base is a square, then the following relationship exist.

Where L represents the length of each side.
This gives

Make L the subject

The area of the base is then calculated as:


The base area is (pi)(r squared).
Answer:
**If the interest is by year then this should work
The interest is $15600 and the amount is $80600.
Step-by-step explanation:
Problem
You deposit $65000 into a bank account paying 6% simple interest per year. You left the money in for 4 years. Find the interest earned and the amount at the end of those 4 years?
Result:
The interest is $15600 and the amount is $80600.