Steps:
(Let x = greater number and y = lesser number)
For this, we will be doing a system of equations. Using the info from the question, our equations are:

So for this, I will be doing the substitution method. Since we know that x = 2y, this means we can replace x in the second equation with 2y as such:

From here we can solve for y. Firstly, subtract 2y on both sides of the equation:

And next, divide both sides by 2:

Now that we know that the value of y is 9, we can substitute it into either equation to solve for x as such:

Answer:
In short, 9 is the lesser number and 18 is the greater number.