If depreciation is 7.25% per year, then the common factor is (1-0.0725), or 0.9275.
Thus, the car's value after 5 years will be:
V = $28000(0.9275)^5 = $28000(0.6864) = $19218.86, or (to the nearest dollar) $19218 (answer)
The proof is because it has a right angle.... I think :)
The polygon would have 24 sides. (n-2)180 = n =24