6- 21 The diagram shows a triangular prism with a horizontal base ABCD. cm 10 cm 18 cm Mis the midpoint of ID). The vertex is vertically above M. DC- 18cm. ВС = 10 см. MI'-7 cm. Calculate the size of the angle between FC and the plane ABCD. Give your answer correct to 3 significant figures. C Diagram NOT accurately drawn