Since P and Q have the same direction, their corresponding components must be in the same proportion, i.e.,
\(\frac{P_x}{Q_x}=\frac{P_y}{Q_y}=\frac{P_z}{Q_z}\)
\(\frac{4}{2}=\frac{-1}{-m}=\frac{8}{4}\)
\(\therefore \,m=\frac{1}{2}\)
Value of m is \(\frac{1}{2}\).