A smartphone company has to decide which battery they will use for their upcoming model. Two battery manufacturers A and B are competing to get the contract. 15 smartphones of the upcoming model were tested with batteries from A. The dataset of talktime on a single charge for them has a sample mean of 7.2 hours and sample variance of 2.7. 31 smartphones of the upcoming model were tested with batteries from B. The talktime on a single charge for them has a sample mean of 6.8 hours and sample variance of 2.9. Assume that the talktime on a single charge for batteries made by A and B are Normal random variables. Based on this information, answer the following two questions.
(a) Compute a point estimate for difference in average talktime of battery A and battery B.
(b) Test whether the battery produced by A results in longer talktime, on average, than battery produced by B. Choose level = 5%.