micro monopoly doubt

[The Villain]

A Monopoly has cost fn c(y)=y^2 and dd curve p(y)=120-y
if we choose a price ceiling for this monopolist so as to maximise consumer plus producer surplus what price ceiling should you choose?
Please tell me how to solve this....please help me wih the soulion>?

[economist]

If you mean maximize sum of consumer and producer surplus, then price ceiling shoul be competitive price, as competitive price axhoeves that.equate price to marginal cost
2y=120-y
y=40
p=80