In order to answer this you first will add 3 hours to 10:30, this is 1:30. Then you need to know what 3/4 of an hour is. An hour is 60 minutes so you just break it into 4 parts, that is 15 minutes per part. so 15 times 2 equal 45 minutes. You add that to 1:30 and get 2:15. That means the arnold family left the beach at 2:15 pm.