What is the length of the outside of a circle called

How do i do this activity, is appreciated

Arandom sample of n = 25 observations is taken from a n(µ, σ ) population. a 95% confidence interval for µ was calculated to be (42.16, 57.84). the researcher feels that this interval is too wide. you want to reduce the interval to a width at most 12 units. a) for a confidence level of 95%, calculate the smallest sample size needed. b) for a sample size fixed at n = 25, calculate the largest confidence level 100(1 − α)% needed.

Aski resort is charging $37.50 to rent a snowmobile for 5 hours. at this rate what will be the cost for a family of 5 to rent snowmobiles for 3 hours on the first day of their vacation and 4 hours for on the last day of their vacation