St. Paul Lumber Company incurs a cost of $280 per hundred board feet in processing certain "rough-cut" lumber, which it sells for $320 per hundred board feet. An alternative is to produce a "finished cut" at a total processing cost of $350 per hundred board feet, which can be sold for $415 per hundred board feet. What is the amount of
(a) The differential revenue,
(b) Differential cost, and
(c) Differential income for processing rough-cut lumber into finished cut?