Solve: 3x+y=153x + y = 153x+y=15 and x+y=7x + y = 7x+y=7.
(4,3)(4, 3)(4,3)
(3,4)(3, 4)(3,4)
(5,2)(5, 2)(5,2)
(4,4)(4, 4)(4,4)