This is a simple question, where the calculation has to be done with clarity for understanding.
Let us assume the unknown number = x
Then we can write the equation as
120x/100 = 160
120x = 160 * 100
120x = 16000
x = 16000/120
= 1600/12
= 133.33
So the unknown number is 133.33. It is not a perfect result but on approximation it can be seen that it is the nearest answer that can be reached. I hope the procedure of doing such problems is clear to you.