Multiply the proportion [both denominator and numerator] by 3, since you have to multiply 20 by 3 to get onehour. Then, whatever is done to the bottom is also done to the top, so 3 by 4 is 12, therefore you have 12 mph.
Step-by-step explanation: 1st you multiply the whole numbers. 2nd multiply denominators (8•9) =72 3rd put into fraction form. So your answer is 54 1/72. Does this make sense?