I didn't get what they mean by that

Tell us what’s happening:

Your code so far

var difference = 12 - 0;

Your browser information:

User Agent is: Mozilla/5.0 (X11; CrOS x86_64 12871.102.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.141 Safari/537.36.

Challenge: Subtract One Number from Another with JavaScript

Link to the challenge:

Setup code:

var difference = 45 - 0;

Challenge requirement:

Change the 0 so the difference is 12.

That is, what do you need to subtract from 45 to get 12?