GMAT Quantitative Reasoning Practice Test 4

Define $\mathit{B}$ as the weight of a button and $\mathit{K}$ as the weight of a buckle.
The total weight of $\left(2\mathit{B}+2\mathit{K}\right)$ is equal to $\left(11\mathit{K}+3\mathit{B}\right)\to 3\mathit{B}=5\mathit{K},\mathit{B}=5\mathit{K}/3$.
The question requires the ratio between $\left(3\mathit{B}+2\mathit{K}\right)$ and $\left(5\mathit{K}+6\mathit{B}\right)$.
The first factor is equal to $\left(5\mathit{K}+2\mathit{K}=7\mathit{K}\right)$.
The second factor is equal to $\left(5\mathit{K}+2\left(5\mathit{K}\right)\right)=\left(15\mathit{K}\right)$.
The ratio between them is $7:15$ and therefore the first factor is $7/15$ of the second one.