To find their mph you would have to divide by 2 to find out how much they got in 1 hour instead of 2. You would have to do 4 2/3 / 2. An easier way to do this is just doing 14/3 x 1/2 which is the same thing except making 4 2/3 a fraction and changing divided by 2 to multiply 1/2. The answer you would get is 14/6, which is 2 1/3 miles per hour. To do this quickly you could just look at the question and divide 4 by 2 to get 2 and then divide 2/3 by 2 to get 1/3 and then add them up.
Hope this helps!