I need a complete solution of this task as I don't understand how we get the correct answer in bold, thanks in advance.

6) Suppose that market demand and supply of protein bars are described by PP(Q) = 400- 5Q and PS(Q) = 120 + 2Q, respectively. After joining the WTO, this country becomes able to import any amount of protein bars at a price of $150 per unit. How many protein bars will it import? a. 60 b. 40 C. 50 d. 15 e. 35