An author is determined to have his first novel published by the publisher of George Orwell's 1984, his favorite book. However, his contract with publisher requires his novel to be at least 75,000 words, and he has written 63,500. Write an equation and determine how many more words he must write.

Well this is quite straightforward.
He needs 75,000 words and has done 63,500 how many more does he need.
Just throw in some abstracts like make words needed be X and words written Y and write an equation from there.