Solve the system: 3x+y=73x + y = 73x+y=7 and y=x+3y = x + 3y=x+3.
(1,4)(1, 4)(1,4)
(2,1)(2, 1)(2,1)
(0,7)(0, 7)(0,7)
(4,1)(4, 1)(4,1)