Suppose the demand d, in units sold, for a company's jeans at price x, in dollars, is d left parenthesis x right parenthesis equals 400 minus 4 x.
a. If revenue equals price times demand, write the rule for the function r(x), which represents the company's expected revenue in jean sales. Then state the domain of this function.
b. If the price is $50, how much revenue will the company earn?

a. The rule for the function r(x) is r(x) = __
nothing.
The domain of the function r(x) is __
b. At a price of $50 the revenue will be $__