The answer is C. You can make a rectangle by putting the diagonals through the center anywhere, but if you want a square, you have to put the two diagonals perpendicular to each other and join their ends. See the diagram.
4 = - 3(2) + c
4 = - 6 + c
c = 10
y = - 3x + 10
Area of parallelogram: lw = 9(5)=45m
Area of triangle: 1/2bh = 1/2(9)(8) = 36m
So total area = 45+36=81m
I'm not totally sure the exact answer, or if this even helps, but the Y intercept is changing from -2 to 5