Final answer:
To express the price p as a function of the demand x, we can substitute the given demand equation into the price-demand equation. The domain of this function is x ≥ 0. The marginal cost is a constant value of 60.
Step-by-step explanation:
To express the price p as a function of the demand x, we can substitute the given demand equation into the price-demand equation: x = 6,000 - 30p. Solving for p, we get p = (6,000 - x)/30. The domain of this function is the set of all possible values of x that make the price nonnegative, so the domain is x ≥ 0.
The marginal cost is the derivative of the cost function with respect to the quantity x. Taking the derivative of C(x) = 72,000 + 60x, we get C'(x) = 60. Therefore, the marginal cost is a constant value of 60.