find the value of a and b

A 3-phase, 2-pole, 50 Hz, synchronous generator has a rating of 200 MVA, 0.8 p.f. lagging. The Kinetic energy of the machine at synchronous speed is 800 MJ. The machine is running steadily at synchronous speed and delivering 50 MW power at a power angle of 10 electrical degree. If the load is suddenly removed assuming acceleration is constant for 10 cycles, the value of the power angle after 5 cycles (in electrical degrees) will be