Solid O-ABCD in a figure is a right quadrangular pyramid.
The bottom is a square and all the length of OA, OB, OC and OD is equal.
Moreover, E and F divide OB and OD into the ratio of 3 : 1, respectively.
The intersection of the plane which passes along three point A, E, F and the side OC is set to G.
Find OG : GC.
Moreover, in two portions of the right quadrangular pyramid divided by this plane, find the volume ratio of the volume of a portion containing O and the volume of the right quadrangular pyramid.