can you please help me with this statistic practice question to revise for my exam, thank you !!

Question 4 (Total: 20 marks) (a) According to the latest manpower report, the average salary of fresh graduates is $2000. You suspect this may not be the case. As such, you checked with 20 friends who have just graduated and their mean salary is $1820 while the standard deviation is $350. You may assume that the salary of fresh graduates is normally distributed. What is the 99% confidence interval for the average salary of fresh graduates? (7 marks) (b) In a recent census report, we noted that, on average, low income households in Singapore spend at least $300 on groceries per month. To verify this fact, we interviewed 20 low income households and determined that the mean monthly grocery bill is $287 and the standard deviation is $80. It is assumed that monthly grocery bill of low income households is normally distributed. Conduct a hypothesis testing using the critical value approach, at the 0.05 level of significance. Is there evidence that the mean monthly grocery bill of low income households as claimed by the report is true? (13 marks)