Griffin Dewatering purchases a wellpoint pump connected to a skid-mounted diesel engine for $14,000. Its market value for salvage purposes decreases 30% each year. When installed on a construction...

Griffin Dewatering purchases a wellpoint pump connected to a skid-mounted diesel engine for $14,000. Its market value for salvage purposes decreases 30% each year. When installed on a construction job, a wellpoint system operates virtually 24/7, and operating and maintenance costs will be $3,500 the first year, increasing $600 each year thereafter. What is the optimum replacement interval if MARR is 15%?