From Mechanics

\displaystyle \begin{align} & m=\text{ }0\textrm{.}0\text{4 }\ \text{kg},\quad u=\text{ 9 }\ \text{m}{{\text{s}}^{-1}}\text{ },\quad v=\text{ 7}\ \text{ m}{{\text{s}}^{-1}} \\ & \\ & I=mv-mu \\ & =0\textrm{.}04\times (-7)-0\textrm{.}04\times 9 \\ & =-0\textrm{.}64\text{ Ns} \end{align}

Magnitude of Impulse = 0.64 Ns