Hello! Need help with this question:

Demand: 145- 5P

Supply: 3P- 15

There is also constant marginal external cost of$20 associated with each purchase.

1. At the market equilibriumquantity, what is the marginal social cost associated withpurchase?
2. At what quantity ofdoes each purchase satisfy allocativeefficiency?
3. Given the marketequilibrium, what deadweight loss with each purchase?
4. When quantity = zero, what is the deadweight loss?