Let's start with a proportion. 2/9= x/18. Now cross multiply. 2 x 18= 36. Now divide 36 by 9 which is 4. So 4 people are eating cookies. You could of also done it this way where you know 9 is a factor of 18. You then multiply both the denominator and numerator by 2 to get 4/18. Your answer would still be 4 people