How Does Gauss's Law Relate R and b When Flux Through a Disk is One Fourth?

[nosracsan]

Homework Statement

A point charge Q is located on the axis of a disk of radius R at a distance b from the plane of the disk (Fig. below left). Show that if one fourth of the electric flux from the charge passes through the disk, then R = sqrt(3)b.

PLEASE SEE ATTACHED WORD DOCUMENT FOR DIAGRAMS!

 

[Doc Al]

Where's your solution? (They give you a big hint.)