The owner of an apartment building can rent all 50 apartments if she charges $600 per month, but she rents one fewer apartment for each $20 increase in monthly rent.

(a) Construct a table that gives the revenue generated if she charges $600, $620, and $640.

(b) Does her revenue from the rental of the apartments increase or decrease as she increases the rent from $600 to $640?

(c) Write an equation that gives the revenue from rental of the apartments if she makes x increases of $20 in the rent.

(d) Find the rent she should charge to maximize her revenue?