please help me with proper explanations. these sum is from testing hypothesis

& An insurance agent has claimed that the average age of policyholders who insure through him is less. than the average for all agents, which is 30 5years A Random sample of 100 policyholders who had insured through him gave the following age distribution. Age last Birthday ( years) No of Person Insured 12 16- 20 22 21 - 25 20 26- 30 31- 35 30 36- 40 16 Jotel 100 Calculate the arithmetic mean and standard deviation of this distribution and use these values to test his claim at the s percent level of significance