Which expression represents the area of a rectangle?

The expression that represents the area of a rectangle is found by multiplying its length by its width. This is because the area measures the amount of space inside the rectangle, and is calculated by taking the length of one side and extending it across the width of the other side. Multiplying these two dimensions gives a total square measurement, which represents the area.

In contrast, the sum of length and width would provide a perimeter measure, not an area. The difference between length and width is not relevant to determining area, as it does not embody the full extent of the rectangle's coverage. Dividing length by width might yield a ratio, but it does not provide the total area. Thus, the correct expression for calculating the area is indeed the product of length and width.