60 Hz generator supplies 0.50 Pmax power to a busbar with infinite power over a conveying line. When a fault occurs, the reactance value between the generator and the infinite bus becomes 400% times the value before the fault. When the fault is isolated, the maximum power that can be transferred by the generator to the endless bus is 75% of the original (initial) maximum value. Accordingly, using the equal area criterion method, calculate the critical clearance angle of the system.