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 \(\frac{1}{2}\).