Rusty Rodes bought an air conditioner with $$200$ down and $60$ equal monthly installments of $$20.$ The total purchase price $($cash price$)$ of the air conditioner was $$1,200.$ Rusty decided to pay off the bill after the $18$th payment. Rusty is entitled to a rebate of which below:a$.$$$18\mathrm{.}98$b$.$$$98\mathrm{.}69$c$.$$$19\mathrm{.}89$d$.$$$99\mathrm{.}88$e$.$$$96\mathrm{.}89$