3nm off track in 30nm along track = 6 in 60: initial track error 6º.  

If the aircraft turns 6º to right it will fly parallel to track but 3nm to left of track.  

It needs to regain the 3nm off track over the remaining 90nm to run: 3 in 90 = 1 in 30 = 2 in 60 so a further 2º alteration to the right is required.