First find how many hours 71/2 hours is. Half of 71 is 35.5. Do one day back... So 35.5 hour becomes 11.5 hours and 2:12 AM still stays the same. Now take away 30 min (0.5) from 11.5 hours and from 2:12 AM. Now the numbers are 11 hours and 1:42 AM. Subtract 1 hour from both amounts, 10.5 hours and 12:42 PM. Now, subtract 11 hours from both amounts again. 0 hours left and 1:42 PM.
