What he did wrong is that he multiplied the denominator wrong. it is supposed to be a 15. Don should re-calculate it to 3 over 15 of a gallon per minute.
First, you have to see how many gallons fill in a minute, obviously, so take 3/4 and divide it by 1/5, which gives 15/4. so you can see, don multiplied the two numbers instead of dividing, which is what he did wrong.Step-by-step explanation: