Answer:
a
, 
b

c

Step-by-step explanation:
From the question we are are told that
The sample data is 21, 14, 13, 24, 17, 22, 25, 12
The sample size is n = 8
Generally the ample mean is evaluated as



Generally the standard deviation is mathematically evaluated as



considering part b
Given that the confidence level is 90% then the significance level is evaluated as



Next we obtain the critical value of
from the normal distribution table the value is

The margin of error is mathematically represented as

=> 
=> 
The 90% confidence interval is evaluated as

substituting values


considering part c
Given that the confidence level is 95% then the significance level is evaluated as



Next we obtain the critical value of
from the normal distribution table the value is

The margin of error is mathematically represented as

=> 
=> 
The 95% confidence interval is evaluated as

substituting values

