[填空题]
A civil engineer is measurin bxmx38v f+wf2mu) i)gpf59w pgfu;*s(o 8o oh5klbo*j 7ya jp4 the area of sloped land to be used for a residential property 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, 5j;o 4 ol7(ubpofysh8 kjo*a* determine the area of the land. $m^2$
