What system of linear equations is represented by the lines shown in the graph?
[Graph description: A coordinate plane with two lines. Line 1 passes through (0,3) and (3,0). Line 2 passes through (0,7) and (2,1). The lines intersect at (2,1).]
x + y = 3; 3x + y = 7
x - y = 3; 3x - y = 7
x + y = 3; x + 3y = 7
x - y = -3; 3x + y = 7
