The answer is B. 24.
A isn't going to work, since 6 is less than 9. It'd give you a negative number.
D won't work, either, it'd give you -15. Again, you'd get a negative number.
C won't work for the same reasons as last time, it'd give you a negative number.
B gives you the exact number we're looking for, and it's a positive number.
