Answer:
Null hypothesis: 
Alternative hypothesis:
And for this case we assume that we have equal variances so that means:

For this case the degrees of freedom are given by:

And replacing we got:

And the best answer would be:
a. 38
Step-by-step explanation:
For this problem we want to test the following:
Null hypothesis: 
Alternative hypothesis:
And for this case we assume that we have equal variances so that means:

For this case the degrees of freedom are given by:

And replacing we got:

And the best answer would be:
a. 38