Final answer:
To find the current value of the used Shelby GT500, subtract the depreciation amount from the original cost. Compare the current value with Marvin's car to determine which car he should buy.
Step-by-step explanation:
To find the current value of the used Shelby GT500, we first need to calculate the depreciation amount. The depreciation amount is equal to the original cost multiplied by the depreciation rate. In this case, the depreciation amount is 8400 * 0.07 = 588. Next, we subtract the depreciation amount from the original cost to find the current value. The current value is 8400 - 588 = $7812.
To compare the current value of the two cars, we need to know the current value of Marvin's car's price is provided. If the current value of Marvin's car is higher than $7812, then Marvin should buy his dad's car. Otherwise, Marvin should buy the used Shelby GT500.