From the problem, we have the demand and supply model.
Demand :

Supply :

a. The number of demand that can be sold at p = $500 is :

The answer is 1356
c. The price which supply and demand are equal. Equate demand and supply :

The answer is $440
b. The number of television when p = 440

The answer is 1716
To summarized, the answers are :
a. 1356
b. 1716
c = $440