If one number exceeds another by 18, the relation between the two numbers is
[tex]x = y+18[/tex]
So, their product is
[tex]xy = (y+18)y = y^2+18[/tex]
This parabola is concave up, so its vertex is its minimum. The vertex lies in [tex](0,18)[/tex].
So, the two numbers are 0 and 18.