A store manager estimates that the demand for an energy drink decreases with increasing price according to the function d(p) = 100/p² + 1, which means that at price p (in dollars), d(p) units can be sold. The revenue generated at price p is R(p) = p · d(p) (price multiplied by number of units).

a. Find and graph the revenue function.

b. Find and graph the marginal revenue R'(p).

c. From the graphs of R and R', estimate the price that should be charged to maximize the revenue.