Question 405685
You know that the area of a rectangle is the length times the width. This is represented by a=lw. 
You're given the area, and you know that two numbers(one times the other) will equal that area. 
Just plug that into your equation. 
18=lw
The best way to do this is to factor 18.
18: 1, 2, 3, 6, 9, 18
There are three pairs of numbers that go into 18. 
{1,18}
{2,9}
{3,6}
When multiplied together, all of those pairs equal 18. So all of those could be your answers, since you're given no more explanation.. 
Hope this helps :)