The system of equations $\left\{\begin{array}{l}{2 x+3 y=7} \\ {5 x-y=9}\end{array}\right.$ is a system of two equations in the two variables _____ and _____ To determine whether $(5,-1)$ is a solution of this system, we check whether $x=5$ and $y=-1$ satisfy each _____ in the system. Which of the following are solutions of this system? $(5,-1), \quad(-1,3), \quad(2,1)$