Allison is saving money to buy a new phone that costs $600 by selling her graphic designs. She is using an app to manage her sales, but it keeps a fraction of each sale. Her net pay is modeled by the function P(x) = x2 + 18x – 160, where x represents the number of sales. How many sales does Allison to make to earn $600?

9 sales
20 sales
38 sales
841 sales