Matrices & Systems · Easy problem

The matrix $A$ has columns $\mathbf a_1 = \begin{pmatrix}1\\0\\2\end{pmatrix}$, $\mathbf a_2 = \begin{pmatrix}3\\1\\-1\end{pmatrix}$ and $\mathbf a_3 = \begin{pmatrix}0\\2\\5\end{pmatrix}$. Using the column picture, find the third (bottom) component of $A\begin{pmatrix}2\\-1\\1\end{pmatrix}$.