IF you are only concerned about gas stations are short selling customers, i.e., you will be happily silent if they pump 1.05 gallon and only charge for 1 gallon. Then, using the hypothesis terms, our H0 becomes mu <=1, H1: mu greater than 1.
Let us assume the volume of gas dispensed for one supposed gallon, denoted as X, follows normal distribution with a known sigma=0.02. And you decide to use X_bar out of 30 measures of one supposed gallon as the test statistic, what are reject region and do not reject region this time using alpha=0.05, respectively? Draw the density function, identify the rejection non rejection region on the graph, and use excel for the calculation.