1. John and George are going to play the guitar tomorrow from 7 o'clock until 10   o'clock. So at 9.30 tomorrow evening they will have been playing the guitar for two and a half hours.
  2. My father are going to paint the house tomorrow from 8 o'clock until 12 o'clock. So at 11 o'clock tomorrow he will have been painting the house for  3 hours.