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 148 by the denominator 12 (which you can enter in any calculator):
148 (numerator) ÷ 12 (denominator) = 12.33
And finally, you get 12.33 as your answer when you convert 9 40/12 (or 148/12) to a decimal.