T test for the difference between means

Backfat thickness is a variable used in evaluating the quality of market hogs. An animal scientist measured backfat thickness (cm) on hogs raised on two different diets, with the following results (see attachment):

Diet 1 Diet 2
_
X 3.49 3.05

Sx 0.40 0.40

Use the t test (a=0.01) to compare the average backfat for the two diets, assuming the number of hogs on each diet was:
a) five
b) fifteen.

The hypothesis that the average backfat thickness for two diets are different has been tested.