Stapleton Manufacturing intends to increase capacity through the addition of new equipment. Two vendors have presented proposals. The fixed cost for proposal A is ​$57 comma 000​, and for proposal​ B, ​$31 comma 000. The variable cost for A is ​$12​, and for​ B, ​$16. The revenue generated by each unit is ​$18. ​a) What is the crossover point for the two​ options? The crossover point for the two options is nothing units. ​(Round your response to the nearest whole​ number.) ​b) At an expected volume of 4 comma 600 ​units, which alternative should be​ chosen? The profit​ (loss) if proposal A is accepted and 4 comma 600 units are produced is ​$ nothing. ​(Round your response to the nearest dollar and include a minus sign if​ necessary.) The profit​ (loss) if proposal B is accepted and 4 comma 600 units are produced is ​$ nothing. ​(Round your response to the nearest dollar and include a minus sign if​ necessary.) ▼ Proposal A Proposal B should be chosen at an expected volume of 4 comma 600 units.