Find the marginal cost marginal revenue and marginal profit

Find the marginal cost, marginal revenue, and marginal profit functions.

C(x) = 3x; R(x) = 9x ? 0.001x2

marginal cost 3

marginal revenue 9-0.002x

marginal profit 6-0.002x


Find all values of x for which the marginal profit is zero. (Enter your answers as a comma-separated list.)
x = ?