(1)
Vr^2 - VsVr + PR + QX = 0
6600^2 - 6600Vs + 300000×0.8 - 145.296×2.4 = 0
Vs = 6583.27v = 6580v

(2)
P=300-500 =200kw
Q=Q1 - 145.3
PR + QX =0
Q1 = 200×0.8/2.4 + 145.3 = 212kvar