$($Time allowance: $5$ minutes$)$ This is a replace now or later problem; however, the question asked is only about one part of the analysis. Do not solve the entire problem, only the part asked below.

You are facing a decision of whether to replace an old equipment at your factory. If the new equipment is purchased, the old equipment can be sold today for $$19.$ However, if the old equipment is not replaced today, it will continue to be depreciated down to zero using straight$-$line method over its remaining $4$ years. The remaining book value today of the old equipment is $$6.$ It is estimated that the old equipment can be sold for $$4$ in one year $($at the end year $1).$ The pre$-$tax maintenance cost $($expenses$)$ per year for the old equipment will be $$7.$ Assume that the discount rate is $10\%$ and the tax rate is $30\%.$

For your answer, round to nearest dollar, DO NOT USE commas to separate thousands, and do not use the dollar $($$$)$ sign; do not enter decimals. For example if your answer is $-$$$12\mathrm{.}534$ then enter $-13$; if answer is $$23\mathrm{.}7459$ then enter $24$ ; if the answer is $-$$$40$ then enter $-40$

The opportunity cost today