Suppose you are testing the null hypothesis that a population mean is less than or equal to 46, against the alternative hypothesis that the population mean is greater than 46. the sample size is 25 and alpha =.05. if the sample mean is 50 and the population standard deviation is 8, the observed z value is:

a) 2.5
b) -2.5
c) 6.25
d) -6.25
e) 12.5