Find the area of the parallelogram with vertices at (1,4), (2,-5), (5,-2) and (4,7)

I know the formula is ad-bc

however how do i work out what the vectors (a,b) and (c,d) are?

its suppose to be (3,3) and (1,-9)

I have drawn a diagram, but it still does not help, what are the non-parallel edges?