$(3$ points$)$ Analyze the following investment options @ $R=3\%,7\%,$ and $10\%-$ show all work $($including units$).$ Show gross and net PV calculations $($ROI not necessary$)$:

a$.$ Incremental cost of $$12,000$; nets total savings of $$14,400$ in year $3.$

b$.$ Incremental cost of $$12,000$; nets savings of $$4,800$ per year for $3$ years.

c$.$ Incremental cost of $$12,000$; nets savings of $$6,000$ in year $1$; returns $$5,000$ in year $2$; returns $$3,400$ in year $3.$