A fraction is usually split into two parts: the first part is the number on top, called the numerator; and the second part is the number on the bottom, called the denominator. These are both separated by a line called the “divisor line”. We can use the division method help to solve this question: to get a decimal, simply divide the numerator 21124 by the denominator 5256 (which you can enter in any calculator):
21124 (numerator) ÷ 5256 (denominator) = 4.02
And finally, you get 4.02 as your answer when you convert 4 100/5256 (or 21124/5256) to a decimal.