$2-11.$ A company has established that the relationship between the sales price for one of its products and the quantity sold per month is approximately $p=75-0\mathrm{.}1D$ units $(D$ is the demand or quantity sold per month and $p$ is the price in dollars$).$ The fixed cost is $$1,000$ per month and the variable cost is $530$ per unit produced. $(2\mathrm{.}2)$