What is the area of a rectangle with a length of 5 units and a width of 4 units?

To determine the area of a rectangle, the formula used is:

Area = Length × Width.

In this case, the length of the rectangle is 5 units and the width is 4 units. By substituting these values into the formula, you calculate:

Area = 5 units × 4 units = 20 square units.

Therefore, the area of the rectangle is 20 square units, which aligns with the correct choice. Understanding this calculation is vital, as it demonstrates how dimensions directly contribute to the overall space contained within a rectangular shape, which is a fundamental concept in geometry.