Answer: The expected revenue for a gallon of gas sold at this station is $3.60.
Explanation:
Since we have given that
Percentage of people who pays by credit card = 20%
= 0.2
Percentage of people who pays by cash =
80% = 0.8
Cost of a gallon of gas paid by card
= $4.00
Cost of a gallon of gas paid by cash =
$ 3.50
So, Expected revenue for a gallon of gas sold at this station is given by

so, it becomes,

Hence, the expected revenue for a gallon of gas sold at this station is $3.60.