Four gallons of gasoline weigh 25 pounds . find the unit rate in pounds per gallon.

There are several information's that are already given in the question. Based on those information's the answer to the question can be easily deduced. 
Weight of 4 gallons of gasoline = 25 pounds
Then
Weight of 1 gallon of gasoline = 25/4 pounds
                                                = 6.25 pounds
From the above deduction, we can easily conclude that the unit rate in pounds per gallon of gasoline is 6.25 pounds/gallon. I hope the answer helps you.

The right answer should be 6 but your not very specific