A particle with a charge of 5.0μC is placed at the corner of a cube. The total electric flux through all sides of the cube is:

Electric flux =Area times the charge enclosed by that Area.

Now for the given situation when charge is placed at the corner of a cube so to draw a Gaussian surface which may include the charge is complex so we will form 7 more cubes meeting their corners at the charge now the charge is at the centre of that bigger Cube and our given cube will contains Q/8 of the charge. As the charge Q is at the corner of the cube three faces are parallel to th Electric field generated by the Charge. Rest 3faces contributes 1/8 part of the total surface area of the bigger cube. And for smaller cube no two flux are in opposite directions so no cancellation. 

Q=5microF

Now Electric flux at all the sides for that bigger cube: