Replacement Time

An outboard motor has an initial price of $2,160. A service contract costs $400 for the first year and increases $150 per year thereafter. The total cost of the outboard motor (in dollars) after n years is given by

C(n)=2160+300n+60n2.

When is the average cost per year at its minimum? This time is frequently referred to as thereplacement time for the piece of equipment. Round to the nearest year.

The replacement time is year .