Respuesta :

9 dived by 3 = 3
so he surfed for 3 hours = 1/3 of 9
and there are 6 hours left 

so he spent 6 hours building a sandcastle 
20 minutes is one third of an hour.
So the rest of the time would be 9 times 60= 540
540-20= 520
520 in hours in minutes would be...
Answer 8 hours and 40 mins!
I hope this helps!