The L−C−R circuit in series combination and phasor diagram is given below
According to the question, Potential difference across resistor, VR=40V Potential difference across inductor, VL=60V Potential difference across capacitor, VC=30V Magnitude of potential difference supplied is given by V=√VR2+(VL−VC)2=√402+(60−30)2 =√(40)2+(30)2=√2500 =50V