To find the perimeter of a rectangle, add the lengths of the rectangle's four sides. If you have only the width and the height, then you can easily find all four sides (two sides are each equal to the height and the other two sides are equal to the width). Multiply both the height and width by two and add the results.
11/21 written as a decimal would be 0.52381 and in percent, it would be 52.381%.
To solve percent, since the total or 1/1 is 100%, we have to remember that the answer is less than 100%. So, we move 2 decimal places right to make it into percent. Then, the answer is 52.381.
To solve percent, you would do 100/21. Then, you would get 4.7619047619. You multiply that by 11 and get 52.381. But, you have to move 2 places left since fractions are tens, hundreds. So, you would get 0.52381.
The correct answer is definitely C.