$8\%$ discount rate, $4-$year lifespan, straight$-$line depreciation, $21\%$ tax rate.

You pay $$100$K for a machine that reduces costs $($increasing revenue$)$ by $$35$K per year for $4$ years. The machine then vanishes without a trace $($or a haulaway cost$).$

What's th NPV of the decision to buy the machine?