The marketing research department of a computer company used a large city to test market the firm’s new laptop. The department found that the relationship between price p (dollars per unit) and the demand x (units per week) was given approximately by

p = 1,296 - 0.12x² 0 < x < 80

So weekly revenue can be approximated by

R(x) = xp = 1,296x - 0.12x³ 0 < x < 80

(A) Find the local extrema for the revenue function.

(B) On which intervals is the graph of the revenue function concave upward? Concave downward?