Out of 15 marbles, 3 are yellow, which leaves 12 more marbles that are NOT yellow. 12/15 would be your answer
hope this helps
(k - 34) x 9 =72
k - 34 = 72/9
k - 34 = 8
k = 8 + 34
k = 42
If they give you the total price and the price after the discount you can use this "formula" to solve it p/100=b/a where p is the percentage, a is the total price and b is the price after the discount.
