Find a suitable set of state variables, derive the state-variable equations, and form the state equation.

\(\left\{\begin{array}{l}\ddot{x}_{1}+\frac{1}{4} \dot{x}_{1}+\frac{2}{3}\left(x_{1}-x_{2}\right)=F_{1}(t) \\ 2 \dot{x}_{2}+x_{2}+\frac{2}{3}\left(x_{2}-x_{1}\right)=F_{2}(t)\end{array}\right.\)