Question 632233
Let y = 0 and solve for x:
3x = 21
x = 7
Let x = 0 and solve for y:
7y = 21
y = 3
Connect the points (7,0) and (0,3).
here's your graph:

 {{{ drawing(500,500,-10,10,-10,10,grid(1),blue(graph( 500, 500, -10, 10, -10, 10, (-3x+21)/7))))}}}