Question 15
Twice the number of marbles in bag $A$ is less than the number of marbles in bag $B$. The sum of the numbers of marbles in bags $A$ and $C$ is less than the number in bag $B$. There are more marbles in bag $D$ than in bag $B$. There are 6 marbles in bag $C$ and 9 marbles in bag $D$. How many marbles does bag $B$ contain?