How to know the delay between vocal track and music track of a song

I have a karaoke song with a vocal and a music track. The vocal track is a number of seconds behind the music track. The wave pattern of the two tracks are quite similar. How can I know how much delay (seconds or milli-seconds) the vocal track is behind the music track? Currently, I use cursor to click the starting points of both tracks, note down the time, calculate the difference and hence the delay. But this method is not accurate as the cursor where I click is not exactly the starting point.

Can somebody help my question?