Asap! which of the following ratios forms a proportion with 4/15? a: 8/20 b: 7/18 c: 12/45 d: 6/25

Acomputer store buys a computer system at a cost of $370.80. the selling price was first at $ 618, but then the store advertised a 20 % markdown on the system. answer parts a and b. a. find the current sale price.