original -.20* original = sales price
original (1-.2) =sales price
original*.8 = sales price
total amount = sales price + sales price*.08
total amount = sales price + sales price*.08
total amount = sales price (1+.08)
total amount = sales price (1.08)
replace original price with p
.8 p =sales price
total amount = .8p(1.08)
total amount = .864p
