Emily has 250 books. If Frank were to double the number of books that he now owns, he would have more than Emily has.

X - the number of Frank's books.

y - the number of Emily's books.

Emily has 250 books:

y = 250

If Frank were to double the number of books that he now owns (2x), he would have more than Emily has (y):

2x > y

2x > 250

x > 250/2

x > 125