Final answer:
The area of a rectangle dilated by a scale factor of 3 is 9 times the original area, hence the correct expression is the original area multiplied by 9.
Step-by-step explanation:
When a rectangle is dilated by a scale factor, both dimensions of the rectangle are multiplied by the scale factor. This means that if the original rectangle has dimensions a and b, after dilation the new dimensions will be 3a and 3b. Since the area of a rectangle is calculated by multiplying its length by its width, the area of the dilated rectangle would be 3a * 3b, which is equal to 9ab. Therefore, the area of the dilated rectangle is 9 times the area of the original rectangle.