From Mechanics

\displaystyle \mathbf{u}=\mathbf{i}+2\mathbf{j} and \displaystyle \mathbf{v}= 6\mathbf{i}-8\mathbf{j} when \displaystyle t=10.

Also

\displaystyle \mathbf{v}=\mathbf{u}+\mathbf{a}t\ gives,

\displaystyle 6\mathbf{i}-8\mathbf{j}=\mathbf{i}+2\mathbf{j}+\mathbf{a} \times 10

\displaystyle 10\mathbf{a}=6\mathbf{i}-8\mathbf{j}-\mathbf{i}-2\mathbf{j}=5\mathbf{i}-10\mathbf{j}

\displaystyle \mathbf{a}=0\textrm{.}5\mathbf{i}-\mathbf{j}\ \text{m}{{\text{s}}^{-2}}