If josiah skateboards from his house to school 4 miles away. It takes him 20 minutes. If josiahs speed, in miles per minute, is constant, what is the constant of proportionality?

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.