From Mechanics

In this case we have \displaystyle \mathbf{u}=0 , \displaystyle \mathbf{a}=2\mathbf{i}+3\mathbf{j} and \displaystyle {{\mathbf{r}}_{0}}=0.

Substituting these into the equation \displaystyle \mathbf{v}=\mathbf{u}+\mathbf{a}t \ \ gives the velocity of the ball at time \displaystyle t=4 \text{ s } as:

\displaystyle \mathbf{v}=0+(2\mathbf{i}+3\mathbf{j})\times 4

which gives

\displaystyle \mathbf{v}=8\mathbf{i}+12\mathbf{j} \ \text{ m}{{\text{s}}^{\text{-1}}}