A student tries to tie ropes, parallel to each other from one end of the wall to the other. If one rope is along the vector $3 \hat{i} + 15 \hat{j} + 6 \hat{k}$ and the other is along the vector $2 \hat{i} + 10 \hat{j} + \lambda \hat{k}$, then the value of $\lambda$ is : (A) $6$ (B) $1$ (C) $\frac{1}{4}$ (D) $4$