The daily rainfall experienced by Soaking City has been recorded on 9 randomly selected days throughout the year. This process has been repeated for every possible combination of 9 days in a year. The standard error of the mean has been calculated and is equal to 0.39 inches. If the rainfall was recorded on 36 (instead of 9) randomly selected days throughout the year, the standard error of the mean would be equal to:____.
a. 0.078 inches.
b. 0.248 inches.
c. 0.045 inches.
d. 3.429 inches.