The time .

Where

is present value of truck, is initial value of truck and is annual rate of depreciation.

Initial value of truck is.

**a.**

Find how much time passed to purchase.

Truck present value is and annual rate of depreciation is .

Substitute , and in .

Change of base formula is .

Apply change of base formula to logarithm expression .

The time to purchase is years.

**b.**

Find how much time passed to purchase.

Truck present value is and annual rate of depreciation is .

Substitute , and in .

Change of base formula is .

Apply change of base formula to logarithm expression .

The time to purchase is years.

**a. **The time to purchase is years.

**b. **The time to purchase is years.

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