How do you solve?

FOR THE NEXT 4 PROBLEMS (#13-16): You want to estimate the average household income for Ohio. You want the margin of error to be no more than $1,000. Prior data shows the standard deviation of household income is $30,000. 13. How many households should we sample to achieve the desired margin of error? 14. Suppose you want to cut the margin of error down to $500 next time. What should your sample size be? 15. Suppose you want to cut the margin down to 1/3 of what it started at (1/3 of 1000). What does your sample sizes have to be? (Be careful!) 16. Why do we always round up when nding the appropriate sample size to achieve a certain margin of error, even when the value after the decimal point is less than .5? (For example, if we solve for n and get 422.2 households, Why do we round this up to 423 households when reporting the required 11?)