Systems of Differential Equations · Easy problem

The vector functions $\mathbf x_1(t)=e^{2t}\begin{pmatrix}1\\1\end{pmatrix}$ and $\mathbf x_2(t)=e^{-t}\begin{pmatrix}1\\-2\end{pmatrix}$ both solve $\mathbf x'=\begin{pmatrix}1&1\\2&0\end{pmatrix}\mathbf x$. Find their Wronskian $W(t)=\det\big[\mathbf x_1(t)\ \ \mathbf x_2(t)\big]$ at $t=\ln 2$.