Answer:
26 1/4 miles per gallon
Explanation:
We are told that the car travels 21 miles per 4/5 gallons. Therefore, the rate at which the car uses the gas is
[tex]\frac{21\text{ miles}}{4/5\text{ miles}}[/tex]
which can also be written as (by taking the reciprocal of the denominator)
[tex][/tex]
