Layer D is the youngest layer
To calculate the mean all you have to do is add all the numbers from the data set and then divide the answer between the number of data set. For example, if you data set is 2,3,4,5,6,then you add 2+3+4+5+6=20 Now you divide 20 between the total number of data, so from 2 to 6 you have 5 numbers. You divide 20/5 and that that is equal to 4.
Since you did not post your data set I can not tell you exactly the answer but you can use this information to walk you through it.
They are able to travel in a vacuum at the same speed.
Hope it helps
