If $\overrightarrow a=\hat i-\hat j+2\hat k, \:\:\overrightarrow b=2\hat i+4\hat j+\hat k\:\:and\:\:\overrightarrow c=\lambda \hat i+\hat j+\mu k$ are mutually $\perp$ then $(\lambda,\mu)=?$

Question

$\begin{array}{1 1} (-3,2) \\ (2,-3) \\ (-2,3) \\ (3,-2) \end{array} $