This can be written as 21/80. You put in 21 shots out of 80 shots. To make it a percent, you first have to make it into a decimal. Just divide the numerator by the denominator and you get the decimal. 21 divided by 80 equals to 0.2625. Now to make this a percent, multiply 0.2625 by 100 or just move the decimal two places to the right. The answer is 26.25. You scored is 26.25%. 26.25 percent is closer to 25, so the final answer is 25.
Hope it helps you :)