Answer: 22.5
Explanation:
First, we will look for patterns in what is given.
We see that 4.5 + 4.5 is 9.
9 + 4.5 is 13.5.
This gives us a rule that each term is 4.5 greater than the one before it (add 4.5 each time). That gives us our answer of 22.5.
So, 18 + 4.5 is 22.5.