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 149 by the denominator 9 (which you can enter in any calculator):
149 (numerator) ÷ 9 (denominator) = 16.56
And finally, you get 16.56 as your answer when you convert 3 122/9 (or 149/9) to a decimal.