I'm going to assume the crust covered by the dosenot matter because the total surface area cannot be found without the depth of the pie.
So the surface are is the area of the top of the pie, the top of the pie is circular and is equal to 2

r²
The diameter is the sum of 2 radii, hence r=8
D=12
= 2r =12
r=8
With the raduis the area can be found
A= 2

r²
A=2

8²
A=2(64)

A=128

If the pie cost 10.99, the cost per inch can be found by dividing the area by cost
cost/inch =128

/10.99
cost/inch =11.64

= 11.64(3.14)
= 36.57
The pie costs 36 cents per square inch
$59.77. Turn the percent into a decimal by moving the decimal to the left two places (7.5 to 0.075). Then multiply the new decimal by the cost (55.60×0.075=4.17). 4.17 would be the total sales tax, so then add it to the price (55.77+4.17=59.77). Hope that helped.
After every month's withdrawals, 4/5 of the original amount at the start of the month will remain. The amount at the start of every month will change. Thus:
an = 4/5 (an-1) ; where a1 = 500.