From Mechanics

\displaystyle \text{100 grams = 0}\text{.1 kg}\ \text{ }\Rightarrow \ \text{ m = 0}\text{.1 }

\displaystyle u = -8 \displaystyle \text{m}{{\text{s}}^{-1}}

\displaystyle v = 5 \displaystyle \text{m}{{\text{s}}^{-1}}

(Note that \displaystyle u and \displaystyle v must have opposite signs as they are in opposite directions.)

\displaystyle \begin{align} & I=mv-mu \\ & 0\textrm{.}1\times 5-0\textrm{.}1\times (-8) \\ & =0\textrm{.}5+0\textrm{.}8 \\ & =1\textrm{.}3\text{ Ns} \end{align}