Hollowing out rectangular prism

Answer

(1) As for the cube whose side is 4 cm, find the volume of the solid made after hollowing out a rectangular prism with rectangle ABCD as a bottom.

(2) As for the solid made in (1), find the volume of the solid made after hollowing out a rectangular prism with rectangle EFGH as a bottom further.

(3) Draw the cut surface in the Fig.2 with hatched lines made when the solid made in (2) is cut by the plane which passes along three point P, Q, and R.

Moreover, find the ratio of the area of the cut surface to the area of the triangle PQR by the least integer.