Subtitle syncher

I have three video files and three subtitle files I want to sync them with. The problem is that the last two subtitle files timings are timed as if all 3 files were one long movie. For example, video File 1 is 1 hour 30 minutes long. Video File 2 is 1 hour 10 minutes long. The beginning of subtitle file one is synched with video file 1 (0 minutes to 1 hour 30 minutes), no problems there. The beginning of subtitle file 2 is 1 hour 30 minutes and 8 seconds and ends with 2 hours 40 minutes. Hopefully that makes sense... so my question is, how can I correct the timings of files 2 and 3 so that they're in sync? Thanks!