Yes, you can use the command t.test as in page 18 of Unit 13 slide.
In this case, your DATA will be infant; so
this needs to be put in the first argument.
the second and third argument can be chose through the form of your alternative hypothesis.
It actually just started working! I have another question. For number 3, part 2, are we supposed to use the significance level to write a conclusion and interpretation? If so, how do we find the significance level?
Now for the #3 part 2, our decision is solely based on the confidence interval.
So, draw a horizontal line, specify zero in the middle and take a look at the location where your confidence interval is.
Page 8 in Unit 11 slide will be helpful for the purpose.
Then, part 3, you can compare this result with the result of hypothesis testing which is related the significance level.