Question 61336
You need to provide more information. l*w is the area of a rectangle.
Sometimes they will tell you something like, the length is 5 more than the width.
The you would say:
let width be: x
Then length is: x+5
Then A=l*w is:
A=x(x+5)
A=x^2+5x
:
Hope that helps.
For the problem in your book, 
let length be: 3x
Let width be:3x-3
A=l*w
A=3x(3x-3)
A=3x(x)+3x(-3)
{{{highlight(A=3x^2-9x)}}}
Happy Calculating!!!