You can put this solution on YOUR website! To find the mean, add up all of the numbers and divide the sum by the number of numbers (which in this case is 6).
So the mean is 4
To find the median, count off about 3 spaces (just take half of the size of the list, which is 6) from the beginning of the list until you hit the middle. Now count count off about 3 spaces from the end of the list until you hit the middle.
-8, -1, , , 7, 18
Since the middle is in between the numbers 3 and 5, add them up and divide that sum by 2.