A new car worth $30,000 is depreciating in value by $3,000 per year. After how many years will the c

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A new car worth $30,000 is depreciating in value by $3,000 per year. After how many years will the cars value be $9,000

Step 1, the question asks for Book Value. Let y be the number of years since purchase.

We setup an equation B(y) which is the Book Value at time y.
B(y) = Sale Price - Depreciation Amount * y

We're given Sale price = $30,000, depreciation amount = 3,000, and B(y) = 9000
30000 - 3000y = 9000

To solve for y, we type this in our math engine and we get:
y = 7

To check our work, substitute y = 7 into B(y)
B(7) = 30000 - 3000(7)
B(7) = 30000 - 21000
B(7) = 9000