How do I determine if it's stastically important difference?

Statistics and Atomic Spectroscopy SECTION A (Answer ONE question, 5%) la) Two students have obtained the following mean values for the same sample using a well established method. Is there a statistically important difference between these two means at the 99% confidence level? Student 1: mean = 78.8 mol/L, 5 measurements Student 2: mean = 83.5 mol/L, 6 measurements The well established standard deviation of the method = 4.0 amol/L 2a) Why are mirrors preferred for focusing light into monochromaters? 3a) Why is ICP-MS the preferred method of determining rare earth elements such as Cerium