Model 1. Suppose the combined abatement for two stationary sources, firmX and firm Y, must total 90 units, and that the MAC functions for these firms are: MACX = 0.8Ax MACY =0.4AY 7) Refer to Model 1 above. The cost-effective solution is: 7) A) AX = 70 and AY = 20 B) Ax = 0 and Ay = 90