Question

according to the Islamic calendar and what year did Muhammad return to Makkah? And what year did Muhammad die? What years were these in the Christian calendar?

Answer 1

       622 is the year when the Islamic calendar begins. It is the year of Hijrah from Makkah to Medina. 
      According to the Islamic calendar Mehammad returned to Makkah in 8 AH ( Anno Hegirae ) or in 629  ( Christian calendar ).
      Muhammad died in 11 AH ( or 632 ).