# shear flow in hollow beam

for shear flow at D , the Q = Ay , i tried another method , i gt 30000 , instead of 29750, why the ans is different from 29750? why cant i use this method( i break the shaded area into 3 parts ( as shown in figure) my working is Q = Ay = (60x10x35) + (2x30x10x150) = 30000

Is my working not acceptable ?