Catch me if you can!

Webber is a police commander. A thief wants to escape. Webber is standing at police station, $0$. The thief is standing at $X$ on the x-axis. The thief starts to run with speed $v_b$ to right, and Webber starts to catch him with speed $v_a$ . When he catches the thief, he comes back to 0 with speed $v_a$. How much time will it take for Webber to catch the thief and back to the police station? ###