What is 21 is 75 percent of what number?

To find the number that 21 is 75 percent of, you can set up an equation using the formula for finding a percentage of a number:

(percentage/100) * number = given number

In this case, we know that 21 is 75 percent of the unknown number, so we have:

(75/100) * x = 21

To solve for x, first simplify the equation:

0.75 * x = 21

To isolate x, divide both sides by 0.75:

x = 21 / 0.75

x = 28

Therefore, 21 is 75 percent of the number 28.