The quantity demanded of a certain brand of DVD player is 3000/wk when the unit price is $485. For each decrease in unit price of $20 below $485, the quantity demanded increases by 250 units. The suppliers will not market any DVD players if the unit price is $283 or lower. But at a unit price of $508, they are willing to make available 2500 units in the market. The supply equation is also known to be linear.

... and you're looking for the equilibrium price? If so,

1. Determine your Demand equation and your Supply equation (both as a function of Price). Your last sentence suggests that they're both linear. Here's a freebie: Demand D as a function of Price p:

D(p) = -12.5p + 9,062.5

2. The equilibrium price is the unique common solution to both equations. Graphically, it's where the two lines cross (intersect), with the Demand line sloping downwards, and the Supply line with a positive slope.

Can you roll with it from here?