A restaurant located in an office building decides to adopt a new strategy for attracting customers. Every week it advertises in the city newspaper. In the 6 weeks immediately prior to the advertising campaign, the weekly grosses were 350, 320, 307, 398, 420, 335 (in million VND). In the eight weeks after the campaign began, the weekly grosses was 488, 301, 276 380, 421, 425 (in million VND).

a/ Test with a = 0.05 to determine whether there is enough evidence to conclude that expected weekly gross after the advertising campaign differs from 382.

b/ Given that the weekly grosses are normally distributed, can we conclude that the advertising campaign helped in improving weekly grosses? (Assuming unequal variances and using a = 0.05)