A hypothesis will be used to test that a population mean equals 10 against the alternative that the population mean is greater than 10 with unknown variance. What is the critical value for the test statistic T₀ for the following significance levels?

(a) α = 0.01 and n = 20 

(b) α = 0.05 and n = 12

(c) α = 0.10 and n = 15