A triangle has vertices A(-2,1,3), B(7,8,-4), and C(5,0,2). Determine the area of triangle ABC.

Vector AB = B-A = [9,7,-7]

Vector AC = C-A = [7, -1, -1]

Area of triangle = (ACxAB)/2

I end up getting vector [-14, -40, -40] and the magnitude is not the correct answer of 35.9 square units. Can someone help?