A large standby electricity generator in a hospital operating room has a first cost of $$75,750$ and may be used for a maximum of $6$ years. Its salvage value, which decreases by $15\%$ per year, is described by the equation $S=75,750(1-0\mathrm{.}15{)}^n,$ where $n$ is the number of years after purchase. The operating cost of the generator will be constant at $$9,000$ per year, and the interest rate is $12\%$ per year. Determine the economic service life and associated AW values.

The economic service life is $$ years and the AW value is $$-$