A Researcher Wishes to Estimate the Average Annual Expenditures Per

A researcher wishes to estimate the average annual expenditures per household on gasoline. The estimate must be accurate within plus or minus $100 and the estimated standard deviation in such expenditures is $500.
Use this problem to answer the following two questions.
-Given estimates and specifications that the population standard deviation is 250, total precision is 100 and the researcher wishes to be 95% confident in the result, the required sample size is

A) 10.
B) 50.
C) 100.
D) 500.
E) none of the above.