[填空题]
A civil engineer is measuring the area of sloped land to be used f t- nb)gopt3p6or a residentdjk2d/uc-ehodi o uto/s:w-q64++mx ial property development project. She uses a total station 6d usdioqo+2dm -kt /wc+-xu4j:h /oe 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. $m^2$
