### Instruction: What is the largest perfect square less than 225 that is a multiple of 9?### Response: I want to find a perfect square that is a multiple of 9 and less than 225.
One way to do this is to start with 225 and subtract multiples of 9 until I get a perfect square.
Another way is to start with the largest perfect square less than 225 and check if it is a multiple of 9.
I think the second way might be faster, so I'll try that.
The largest perfect square less than 225 is 196, which is 14 squared.
But 196 is not a multiple of 9, so I need to go smaller.
The next perfect square smaller than 196 is 169, which is 13 squared.
But 169 is not a multiple of 9, so I need to go smaller.
The next perfect square smaller than 169 is 144, which is 12 squared.
And 144 is a multiple of 9, so I found it!