Since the slope of a line is (change in y)/(change in x), we can plug (-2, 4) and (-4, -2) in to get (-2-(-4))/(4-(-2))=(-2+4)/(4+2)=2/6=1/3, making our equation
y=(1/3)x+b from y=mx+b. Plugging (3, -2) in from there, we get -2=(1/3)*3+b=1+b. Subtracting 1 from both sides, we get b=-3, making our equation y=(1/3)x-3 due to that y and x stay variables