A store sells 600 boxes of chocolates each week at an average price of $8 a box. Due to rising costs, the owner wants to raise the price of each box. She figures she will sell 40 fewer boxes for every $1 she raises the price. Write a function T(x) for her total sales after raising the price of each box by x dollars. What is the maximum amount that she can increase the price per box without having total sales fall below the current value of $4800?