Question

3 h 6 min 45 sec+8h 55 mins 20 sec

Answer 1

Convert them both to minutes to get: 186 mins and 45 sec + 535 mins and 20 sec

Add to get: 772 mins and 5 sec

Answer 2

   3 hours . . . 6 minutes . . . 45 seconds
+ 8 hours . . 55 minutes . . . 20 seconds
  ________________________________
 11 hours . . 61 minutes . . . 65 seconds

But 65 seconds = 1 minute . . . 5 seconds

 11 hours . . 62 minutes . . . 5 seconds

But 62 minutes = 1 hour . . . 2 minutes

 12 hours . . 2 minutes . . . 5 seconds


I think this is regrouping, but with 60s instead of 10s.