Anbspsolve for the equilibrium price p and quantity q

Question

Suppose that demand for good X is given by:Q^D = 20 -P, while supply is given by: Q^S = 2P-4.

a) Solve for the equilibrium price (P^*) and quantity (Q^*)

b) Suppose the government sets a price ceiling of $6. What is the shortage that results from this price ceiling?

c) Now suppose that, instead of a price ceiling, the government charges an excise tax of $3 per unit. Solve for the new equilibrium price and quantity after this tax is imposed, and the amount of revenue raised by the government.