Answer
Red line: $3x+y=6$
Green line: $-3x+y = 6$
Blue line: $3x-y =6$
The red and green lines have the same intercept (6), and the green and blue lines have the same slope. The blue line has a different intercept (-6), and the red line has a different slope (-3).
Work Step by Step
red line:
$3x + y = 6$
$3x + y -3x = 6-3x$
$y = -3x + 6$
green line:
$-3x+y = 6$
$-3x+y +3x = 6+3x$
$y = 3x + 6$
blue line:
$3x-y =6$
$3x - y +y -6 = 6 + y - 6$
$3x - 6 = y$
