There are 144 square inches in one square foot. Therefore, price per square inch = price per square foot / 144.
Remember the formula for the area of a circle is 3.14*radius*radius.
Total amount needed = amount needed per person * number of people
Number needed = total amount needed / size of each one
Total cost = total size in square inches * cost per square inch
Sample Answer
You should check your program with this sample. If there are 10 people the following costs and amounts would be involved.
Parts one and two are easier, I suggest you try those first.