Table D represents a linear function.
If you mean what goes in the blanks, it is 5 for the first empty box and 10 for the second empty box.
The mean is 27
How you do this is you add all the numbers together even the ones that are duplicated like in this case 31. Now add em all up which equals 135. Now you take the number that they equal up to and divide by how many numbers are in the set of data in this case it is 5. After dividing you get 27.
I hope this helps!