A company has surveyed 40 customers who shop on a particular online commerce platform and the company has collected data on the change in monthly shopping volume measured in dollars following an advertising campaign. They found that the average increase in spending to be $23 with sample standard deviation of $14.

The company expected the advertising campaign to effect a change in average spending of less than $30.

Test the compay's expectation by using the p-value method at the 5% significance level.

You need to

(a) justify your testing approach, (b) define any new notations properly, (c) state the null and alternative hypotheses, (d) show proper statistic for the test and steps of derivation, (e) make decision for the test and add a brief interpretation.