Since the formula is 

Length x Width = Area

and the Area is 24

Then 

Length x Width = 24

Just think through your multiplication facts that

you learned in 3rd or 4th grade, and

come up with three pairs of numbers that 

when multiplied gives 24:

 L x W = 24

12 x 2 = 24 

 8 x 3 = 24

 6 x 4 = 24

So when the length is 12 and the width is 2, draw this rectangle,
which is 12 units across and 2 units high:

 

And when the length is 8 and the width is 3, draw this rectangle,
which is 8 units across and 3 units high:




And when the length is 6 and the width is 4, draw this
rectangle, which is 6 units across and 4 units high:



Count the little squares (square units) inside each of the 
three big rectangles above and you will see that each one has
exactly 24 of those little square units in it.  That's what
area is all about.  The area is just how many of those 
little square units that will fit inside a rectangle.

But you don't have to draw the 24 square units as I have
above, you can just draw the rectangles without showing
the square units of area:

So when the length is 12 and the width is 2, just draw this rectangle
without showing the 14 square units of area that will fit inside the 
rectangle::

 

And when the length is 8 and the width is 3, just draw this rectangle
without showing the 24 square units of area that will fit inside the 
rectangle::



And when the length is 6 and the width is 4, draw this
rectangle without showing the 24 square units of area
that will fit inside the rectangle:

 

Edwin