Answer: 
Step-by-step explanation:
The area of a rectangle can be calculated with this formula:

Where "l" is the length and "w" is the width.
You can identify from the figure that the length and the width of this rectangle are:

Then, you need to substitute this lenght and this width into
:

Now, apply Distributive property:

Finally, you need to add the like terms. Then, you get:
