What is this simple rational function?

A home security system costs $9/month in electricity costs (you may assume this is a fixed cost over the duration of the time involved in this question). A new security system costs $1500 to purchase and lasts for 8 years.

Determine a rational function that gives the annual cost of a security system as a function of the number of years you own the system. Using this function determine the average annual cost of the security system given above.

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C(x)=(1500+108n)/n, where n is the number of years, would be the rational function that gives the annual cost of the security system.

What about the average annual cost of the security system given above ?

Would it be C(8)=(1500+108(8))/8?