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 111 by the denominator 18 (which you can enter in any calculator):
111 (numerator) ÷ 18 (denominator) = 6.17
And finally, you get 6.17 as your answer when you convert 3 57/18 (or 111/18) to a decimal.