The formula to calculate the motional emf induced in a moving conductor in a magnetic field is given by

$\epsilon =Blv ...\left(1\right)$

Substitute the values of the known parameters into equation (1) and solve to calculate the required velocity of the rod.

$\begin{array}{rcl}0.08 \mathrm{V}& =& 0.4 \mathrm{T}\times \left(10 \mathrm{cm}\times \frac{1 \mathrm{m}}{100 \mathrm{cm}}\right)\times v\\ & \Rightarrow & v=\frac{0.08 \mathrm{V}}{0.4 \mathrm{T}\times 10 \mathrm{cm}\times \frac{1 \mathrm{m}}{100 \mathrm{cm}}}\\ & =& 2 \mathrm{m} {\mathrm{s}}^{-1}\end{array}$