[填空题]
A civil engineer is measuring the area of sloped land o3mfyg mi8ei4vkob7r2,(7s u to be used for a resiif b(m n-n5ju2dential -nmi5 2fjnu( bproperty development project. She uses a total station theodolite device to determine the coordinates of the corners of the land and finds them to be (15,25,9),(20,5,5),(-10,-10,2) and (-15,10,6) where the coordinates are in metres from a fixed origin where she is standing. Using vectors, determine the area of the land. $m^2$
