In the area model of a square with side (x + 3), what will the four parts be?

Correct answer: x^2, 3x, 3x, 9

The correct answer is A: x^2, 3x, 3x, and 9. Split each side of the large square, whose side is x+3, into lengths x and 3. This creates four regions: an x-by-x square with area x^2; one x-by-3 rectangle with area 3x; another 3-by-x rectangle with area 3x; and a 3-by-3 square with area 9. Adding them gives x^2 + 3x + 3x + 9 = x^2 + 6x + 9, which is (x+3)^2. Option A lists exactly these four geometric parts. Option B combines the two rectangles into 6x and then incorrectly lists an extra 9, so it does not show four correct regions. Option C includes 12, which is not the area of any required part. Option D gives x as though it were an area of a strip, but the rectangle must have area 3x. Memory cue: for (x+3)^2, the two mixed rectangles are each 3x, not 6x.