Chapter 2.2, Problem 5E

Solve the equation $Ax=b$, where $A=\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 1& 3& 1& 0\\ 4& 1& 2& 1\end{array}\right]\left[\begin{array}{cccc}2& 1& 0& 0\\ 0& 1& 2& 0\\ 0& 0& -1& 1\\ 0& 0& 0& 1\end{array}\right]$ and $b=\left[\begin{array}{c}1\\ 1\\ 2\\ 0\end{array}\right]$.