A plant physiologist is planning to measure the stem lengths of

  
A plant physiologist is planning to measure the stem lengths of soybean plants after 2 weeks of growth when using a new fertilizer. Previous experiments suggest that the standard deviation of stem length is around 1.2 cm. 
(a). how many soybean plants the researcher should have if she wants the 99% confidence interval to have width less than 0.5.
(b). how many soybean plants the researcher should have if she wants the 99% confidence interval to have margin of error than 0.3.