first you have to get it to y intercept for which is y=mx+b so you would subtract 7x and bring it to the other side so now u have -3y=7x+21 next u would divide -3 to get y alone so u would have now is y= -7/3x+ 7 then when u graph it the y intercept is 7 so u graph 7 on the y axis and the slope is -7/3 so u would go down 7 and over 3