经济学的一个小问题啊.Suppose that the market demand curve for haircuts

经济学的一个小问题啊.
Suppose that the market demand curve for haircuts in some town is
(假设某镇的理发市场需求曲线是）
D=80-2p+5i
where D is quantity demanded per month.P is price per haircut and i is consumer income(in tens of thousands of euros).the supply curve is
（D指每月需求数量,P指每次理发价格,i 指消费者的收入（数以千计的欧元）.供给曲线是：）
S=4P
where S is the quantity supplied per month.
（S指每月供给数量）
Q:Suppose i=3 .Find th equilibrium price and quantity of haircuts?
（问：如果i=3 .找出处于平衡点的价格和数量是多少?）