A granary purchases a conveyor used in the manufacture of grain for transporting, filling, or emptying. It is purchased and installed for \($70,000\) with a market value for salvage purposes that decreases at a rate of 20 percent per year with a minimum of \($3,000.\) Operation and maintenance is expected to cost \($14,000\) in the first year, increasing by \($1,000\) per year thereafter. The granary uses a MARR of 15 percent. What is the optimum replacement interval for the conveyor?