Miles paid $5824, including 4% sales tax, for an out-of-state purchase of a car. in order to calculate the amount of sales tax he owes in his state, he must first determine the price of the car without sales tax. how much did the car cost before sales tax? this one is a little bit tricky. the amount you need to find the sales tax of is not know. let the original price be x. then, 4% of that price is 0.04x. adding the original price and the sales tax, we get the amount paid. therefore, the equation is x + 0.04x = 5824