The following is a system of two linear equations in two variables. $\left\{\begin{array}{r}{x+y=1} \\ {2 x+2 y=2}\end{array}\right.$ The graph of the first equation is the same as the graph of the second equation, so the system has _____ solutions. We express these solutions by writing $x=t$ $y=_____$ where $t$ is any real number. Some of the solutions of this system are $(1,-),(-3,-),$ and $(5,-)$