12. Find the critical value to test the hypothesis that the change in advertising has increased sales, using a=0.05. a. -1.895 b. 2.365 c. -1.860 d. 2.306 13. If the decision for this test is to fail to reject the null hypothesis, what is the appropriate conclusion? a. the change in advertising did increase sales significantly b. sales have not changed at all from last year to this current year c. there is not sufficient evidence to indicate that the change in advertising increased sales d. sales have decreased from last year to this current year