Ford Motor Company was able to reduce by $74\%$ the cost required for installing data acquisition instrumentation on test vehicles by using MTS$-$developed spinning wheel force transducers. The cost this year $($i$.$e$.,$ end of year $1)$ is expected to be $$3500.$

If the costs are expected to increase by $$250$ each year for the next $4$ years, what is the equivalent annual worth of the costs $($years $15)$ at an interest rate of $7\%$ per year?

The equivalent annual worth is $