Elise's number is 29.
If you think of multiplying a value by -3 to get -33, it would obviously be 11.
So in this case, you would want to add 18 to 11 to get Elise's number, which is 29. Subtracting 18 from 29 would get you back to the value of 11, which you can then multiply it by -3 again to get -33.
