$12\mathrm{.}19$ A synchronous generator is connected directly to an infinite bus. The voltage of the infinite bus is $15$ kV$.$ The excitation of the gnerator is adjusted until the equivalent field voltage Ef is $14$ kV$.$ The synchronous reactance of the machine is $5$ Ohms. Compute the following: a$.$ Pullover power $($maximum power$)$ b$.$ Equivalent excitation voltage that increases the pullover power by $20\%.$