Kite wxyz is graphed on a coordinate plane. what is the area of the kite?

The answer 
according to the image, we can compute the area of the kite as follow:
Area =  (D x d ) / 2

D is the great diagonal,
d is the little diagonal

D = XZ and d = WY

let's find XZ,
vector XZ = (3-3, -4-4) = (0, -8), so  XZ = sqrt( 0² +8²) = 8
vector WY = (5-1, 1-1) = (4, 0), so  XZ = sqrt( 0² +4²) = 4

finally  the area  A = 1/2(D xd) = 1/2(8x4)= 32/2=16 
the area is 16 unit²

Ithink it is correct but just ask someone else but i am sure it it