Positive Externality

The market for jelly has a supply and demand given by the following:

Q_D=200-10p

Q_S=20p-100

The consumption of jelly creates a positive externality with marginal external benefit of:

MEB = 20-0.025Q

1. Suppose a subsidy is used to eliminate the inefficiency from the externality. What subsidy would lead to the efficient output?
2. With the subsidy, find the price consumers pay and price sellers get.
3. What is the PS, CS, Government expenditure, and Total external benefit with the subsidy?
4. Show that the deadweight loss matches the difference in welfare between (b) and (g).