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 21 by the denominator 47 (which you can enter in any calculator):
21 (numerator) ÷ 47 (denominator) = 0.45
And finally, you get 0.45 as your answer when you convert 21/47 to a decimal.