Question $2$

A vole$-$rigging machine purchased $3$ years ago for $$40$ provides adequate service, but an improved version for S$3$S is now available that will reduce operating costs and cut inspection expenses. The table shows costs and salvage values for the two machines, and does not include costs that are the same for either machine. If you need a vote$-$rigger for only $4$ more years, and a $15\%$ required rate of retum, should you replace the current one? Clearly state which approach you use $($opportunity$-$cost or casb$-$flow$)$ and type of equivalence calculation $($present$-$worth, equivalent annual cost, etc.$).$

$\backslash$table$[[,$Defender $0,$Collenger C$],[$Year$,$Operating cost, S$,$Salvage value, S$,$Operating cost S$,$Sulage value, S$],[0,,12,,35],[1,3\mathrm{.}40,7,020,30],[2,3\mathrm{.}90,4,1,27],[3,4\mathrm{.}60,250,120,24],[4,5\mathrm{.}60,1,150,20],[5,,,2,17],[6,,,2\mathrm{.}60,15]]$

$[$IS$]$