Here is the right image, sorry again!

Sorry, here is the right file

Use a tabular form to test all combinations. The lowest sum of numbers a, b and c such as a+b+c=18 is

6+6+6=18

`6^2+6^2+6^2=108`

For three different numbers, the smallest sum of squares is for:

5+6+7=18

`5^2+6^2+7^2=110`