In a sample of n 15 lichen specimens, the researchers found the mean and standard deviation of the amount of the radioactive element, cesium-137, that was present to be 0.009 and 0.005 microcurie per illiter, respectively. Suppose the researchers want to increase the sample size in order to estimate the mean μ to within 0.001 microcurie per milliliter of its true value, using a 95% confidence interval. Complete parts a through c. a. What is the confidence level desired by the researchers? The confidence level is b. What is the sampling error desired by the researchers? The sampling error is c. Compute the sample size necessary to obtain the desired estimate. The sample size is(Type a whole number.)