A dog escapes from his front yard at 3.15 p.m. and is discovered 3.5 miles from home at 4:50 p.m. What is the dog's average speed in miles per hour?

Please let me know if this is correct, if is not, let me know what I did wrong.

speed=d/time of travel
3.5/1.35 = 2.59 m/h

Not quite. Since there are 60 minutes in an hour, 1 hour and 35 minutes is 1.583 hours, not 1.35.

The correct answer is 2.21 miles/h