The line y=mx+b forms a triangle with the axes. The intercepts are y intercept=b and x intercept=-b/m.
The area of the triangle is (1/2)(b)(-b/m)=9. Therefore m=-b^2/18.
So we have y=-b^2x/18+b. Plug in x=-2 and y=4: 4=2b^2/18+b.
36=b^2+9b or b^2+9b-36=0=(b+12)(b-3) and b=3 or -12, and m=-9/18=-1/2 or -144/18=-8.
It appears we have two lines: y=-x/2+3 (red) or y=-8x-12 (blue).
They intersect at (-2,4) in quadrant 2. The areas of the triangles in quadrants 1 and 3 = 9 square units.