The given pattern starts with an 18, then we have a 12, we can go from 18 to 12 by subtracting 6 from the initial number. By subtracting 6 from 12, we get the number that goes on the right side of 12, that is:
12 - 6 = 6
Then, fill the missing number with a 6.
18, 12, 6, 0
