Halliday, Resnick & Walker — Electromagnetic Oscillations and Alternating Current: Problem 14

14 An alternating source drives a series $RLC$ circuit with an emf amplitude of $10.0\text{ V}$, at a phase angle of $+30.0^\circ$. When the potential difference across the capacitor reaches its maximum positive value of $5.00\text{ V}$, what is the potential difference across the inductor (sign included)?