There are 60 minutes in 1 hour.
This is a very important fact, that you must learn.
This means that:
There are 30 minutes in ½ an hour (÷ 2)
There are 15 minutes in ¼ an hour (÷ 4)
There are 120 minutes in 2 hours (x 2)
There are 135 minutes in 2¼ hours (add last two lines together)