A conveyor system costs $80,000 to install. The salvage value of the conveyor system decreases by $13,000 each year until its salvage value is $0, at which point it no longer decreases. The cost to operate and maintain the conveyor system the first year is $13,000; this cost increases by 7% per year. What is the optimal replacement interval and minimum EUAC for the conveyor system, assuming a MARR of 10% is used?