The controller for Mercer Manufacturing is trying to implement some of the characteristics of a just$-$in$-$time $($JIT$)$ inventory system. She has accumulated data on Mercer's present inventory system and obtained some projections and estimates of what the results of a JIT system would be$.$ Annual direct material requirements are estimated as $360,000$ units. Estimated per$-$unit costs for various order sizes are presented below: The inventory holding cost is estimated at $\backslash (\backslash$$ $0\mathrm{.}75\backslash )$ per unit, per month. Mercer currently purchases $120,000$ units every four months. Under a JIT system Mercer would purchase $30,000$ units every month. The monthly inventory schedule and the controller's estimate for a JIT system are provided below: $($Assume the above trend continues throughout the rest of the year.$)$ Required: Which system should Mercer use, and why? Show calculations in support of your recommendation.