[SOLVED] Linear Applications help

A small theatre has a seating capacity of 2000. When the ticket price is $20, attendance is 1500. For each $1 decrease in price, attendance increases by 100.

a). write a linear funtion of A(X) and specify the domain of the function

b). write a funtion that represents the revenue, R(X) as a funtion of ticket price, x. Specify the appropirate domain of the function.

So for the linear functon of A(x), I put it as:

A(x) = 20x , 0 is less than or equal to x and less than or equal to 1500.

but I don't know if this would be right.

and for b). I can't think of a function that would work for it. I've tried using my graphing calculator but I keep getting negatives.

Edit: Took me 2 hours but I finally solved it!