From Mechanics

\displaystyle \begin{align} & \mathbf{v}=\frac{d\mathbf{r}}{dt}=40\mathbf{i}+(6t+20)\mathbf{j} \\ & \mathbf{v}(10)=40\mathbf{i}+(6\times 10+20)\mathbf{j}=40\mathbf{i}+80\mathbf{j} \\ & v(10)=\sqrt{{{40}^{2}}+{{80}^{2}}}=89\textrm{.}4\text{ m}{{\text{s}}^{\text{-1}}} \\ \end{align}