$6:40$ - $4:30$ = $2$ hours $10$ minutes 
We left for a summer camp at $4:30$ PM and got to our destination at $6:40$ PM. How long did we travel?~ 
Options:
  $1$ hour $40$ minutes 
  $2$ hours $10$ minutes 
  $2$ hours $20$ minutes 
  $1$ hour $50$ minutes 
  $50$ minutes 