Haven't you forgotten something important? Order of operations. You have to do the multiplication before the addition. So you multiply 2 by 6 first then add 9: 9+12=21. Now you need to tell the person who gave you Best Answer that you made a mistake! A lot of people make the same mistake, so don't be put off. You will get it right next time! Remember you do brackets (parentheses) first (work out what's in the brackets first), then you do multiplication and division, then you do addition and subtraction. It's like having a glass of soda. If you pour the soda before putting the glass in place, you get soda all over the floor! So you put the glass in place first then pour the soda!