Exercise 10.4.2

Let $B=\left\{\left[\begin{array}{r}1\\ -1\\ 2\end{array}\right],\left[\begin{array}{r}2\\ 1\\ 2\end{array}\right],\left[\begin{array}{r}-1\\ 0\\ 2\end{array}\right]\right\}$ be a basis of $\mathbb{R}^{3}$ and let $\mathbf{x}=\left[\begin{array}{r}5\\ -1\\ 4\end{array}\right]$ be a vector in $\mathbb{R}^{2}$. Find $\left[\mathbf{x}\right]_{B}$.