The answer is:
g-17
Whenever you come across a question that says "What is this number less than this other number," you always take the number that was said last, then place a subtraction sign after it, and then place the number that was said first after that subtraction sign.
Another example would be:
What is 5 less than a number Y ?
First you must take the number mentioned last. That would be Y. Now, since the example question states "less than," you must put a subtraction sign after Y. Lastly, place the number that was said first after that subtraction sign.
The answer to the example question would be:
Y-5
