H1B Cap Exemption eligibility.

Hi All,I have an expired, unused approved H1B that employer A filed for me in 2008. Its validity is from 1st Oct 2008 to 15th Sept 2011. I never used it, never worked in that visa. I came here on H4 in 2009 and was on that visa until Jan 2014. Since Jan 2014 I have been on F1. Employer B(who I work for now) is filing my H1 this year. I want to know if I am eligible for cap exemption. If so, will those 3 years be subtracted from the actual 6 and will I be given only 3 more years towards my total H1 period?FYI - My STEM OPT expires in June this year. I also have the approved I-797 from the old H1.Thanks a lot for the help, I appreciate your time in replying to my post.