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