The total cost function of a firm is given by where the selling price per unit is given as ₹ . Find…

The total cost function of a firm is given by $C(x) = \frac{1}{3}x^3 - 5x^2 + 30x - 15$ where the selling price per unit is given as ₹ $6$. Find for what value of $x$ will the profit be maximum.