To calculate the perimeter of a rectangle, you use the formula:

$\text{Perimeter} = 2 \times (\text{Length} + \text{Width})$

Given:

• Length = 21 meters
• Width = 11 meters

Now, plug the values into the formula:

$\text{Perimeter} = 2 \times (21 + 11) = 2 \times 32 = 64 \text{ meters}$

So, the correct answer is 64 m.

Would you like more details or have any questions about this?

Here are 5 related questions:

1. How would you calculate the area of a rectangle?
2. What is the perimeter of a square with side length 21 meters?
3. How does changing the length or width of a rectangle affect its perimeter?
4. How would you calculate the perimeter of a triangle with given side lengths?
5. If a rectangle's perimeter is 64 meters and its length is 21 meters, what is its width?

Tip: Always remember to double the sum of the length and width for the perimeter of a rectangle.