At resonance, the frequency of supply power equals to naturan frequency of LCR circuit. Impedence, $$Z=sqrt{R^2+(omega L-1/omega C)}$$ $$omega_L=dfrac{1}{omega_C}$$ so, $$Z=R$$ $$I=V/R=200/20=10 A$$ Power, $$W=V imes I=200 imes 10=2000 W$$