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 129 by the denominator 31 (which you can enter in any calculator):
129 (numerator) ÷ 31 (denominator) = 4.16
And finally, you get 4.16 as your answer when you convert 2 67/31 (or 129/31) to a decimal.