I don't entirely remember how these concepts go; the information is muddled by a few other topics. The question is listed below, word for word.

The demand and supply for a good are given by the linear functions

D=30-2p-y, S=p,

where D is the quantity demanded, S is the quantity supplied, p is the price, and y is the aggregate consumers' income, which is exogenous. Denote the equilibrium quantity by Q and the equilibrium price by P.

(i) Find the effect of a change in income on equilibrium price and quantity, that is, \frac{dQ}{dy} and \frac{dP}{dy}, by the method of implicit differentiation.

(ii) Check the result by first solving for the equilibrium price and quantity explicitly and then finding \frac{dQ}{dy} and \frac{dP}{dy}.

(iii) Repeat (i) and (ii) for the following demand and supply functions

D=a-bp+cy, S=\alpha+\beta p,

with a>0, b>0, c>0, \alpha>0, \beta>0, \alpha<a+cy.

I'm doing my best to try and remember how this all works, but some help on the subject would be appreciated.