Answer:

Area of rectangle = (3x + 7) (3x - 7)

Area of rectangle is

the unit should be

cm^2

Step-by-step explanation:

1. multiply 3x and 3x you get 9x^2

2. multiply 3x and -7 you get -21x

3. multiply 7 and 3x you get 21x

4. multiply 7 and -7 you get -49

5. you now have 9x^2 - 21x + 21x - 49

6. when you subtract 21x to -21x you get 0

so you can just cancel out -21x and 21x from the equation then you get the area of rectangle which is 9x^2 - 49