I'm trying to solve for C and D, but I don't know what to do. Please show steps and answers for each one.

5. Find the critical values ("z", x2 or "t" scores) for the following a. (1pt.) C.L. = 98%, n is 25 and o is unknown. b. (1pt.) Alpha is 10%, the sample size is.45 and sigma is known. c. (1pt.) df = 28, alpha = 0.005 (find the left tail value). d. (1pt.) n = 18, degrees of freedom = 17 and a = 0.05. (x- and x z)