b) The contribution margin is the difference between total sales revenue and the variable costs. The idea of segment contribution margin is that it covers the fixed expenses, whether controllable by the segment or not.
When you use the incremental cost allocation method, you must rank cost activities and how they will be allocated. In this case, department 2 is the primary user, and therefore, rental costs must be allocated first to them. Rental costs will be allocated at a $25/hour rate.
Since department 1 is the next user, 100 hours will be allocated using the same rate as department 2, but the next 200 hours will be allocated at the lower $22/hour rate. Total rental cost allocation to department 1 = (100 x $25) + (200 x $22) = $2,500 + $4,400 = $6,900