I don't understand how to solve this question. How can q = p when demand has a negative slope, and supply does not in a competitive market? Can someone explain this both mathematically and conceptually?

In a competitive market the demand curve is given by P = 120 - 2q and supply by P = q. What are the consumer surplus (CS) and producer surplus (P5) in the market equilibrium? 0 C5 = 3200, PS=1600 0 C5 = 1600, P5 = 800 0 C5 = P5 = 1600 0 C5 = 2400, PS: 1600 0 None of the above