Which equation is the correct equation and why? pls

The answer is C

as there are two squares and their value is represented by a variable (x) both or them multiplied for the area is x to the power of two or x squared. After that both have a length of 3 yet the one that's is not shades is considered negative as it is not part of the whole. Those multiplied you end up with negative 9. Which leaves you to the equation

after that you have to solve this binomial or factor it. If you notice this binomial fits the difference of squares rule. Leaving your answer to be