Solve using substitution: {x+y=7y=2x\begin{cases} x + y = 7 \\ y = 2x \end{cases}{x+y=7y=2x
x=frac73,y=frac143x = \\frac{7}{3}, y = \\frac{14}{3}x=frac73,y=frac143
x=2,y=5x = 2, y = 5x=2,y=5
x=3,y=4x = 3, y = 4x=3,y=4
x=5,y=2x = 5, y = 2x=5,y=2