*It's debatable that there are 2 answers to this question because of how it's worded*
For the first answer:
There would be 66 books left.
To get this, you need to multiply the original amount (120) by the decimal form of the percentage.
So, to get the decimal form you need to divide by 100, which essentially means you move the decimal 2 places to the left.
55% then becomes .55
So, 120 * .55 = 66
For the second answer:
If the question means that you need to decrease 120 by 55% of 120 then the answer would be 54.
120 - 66 = 54
So, depending on the answer choices and how it's interpreted, do what you will with this information.
