compare two cell phone companies and determine which is the better deal. Needs to be in a y=mx+b equation for each company.

company a $40 base rate plus every minute costs .05
company b base rate $30 plus every minute costs .07
based on 800 minutes

PLEASE HELP ME ASAP!

a = 800(.05) + 40

a = $440

b = 800(.07) + 30
b = $590