CONSIDER THE CUBE AS SHOWN AND A CHARGE AT ITS CORNER..TO COMPLETE THE GAUSSIAN SURFACE YOU NEED SEVEN MORE CUBES.THUS THE NET FLUX THROUGH WACH CUBE WILL BE Q/8.

(NOW IMAGINE BIG CUBICAL ROOM AT THE CORNER OF WHICH IS PLACED A LIGHT SOURCE(IN OUR CASE ITS Q/8)).CLEARLY THE LIGHT CANT PASS PARALLEL WAYS SO IT WILL PASS THROUGH THE THREE OPPOSITE FACES.HENCE THE TOTAL FLUX IN OUR CASE WILL BE DIVIDED BY THREE.IE.Q/24.