Electronics help recitifier with a zener diode

[badaboom]

Homework Statement

Design a rectifier with a zener diode that satisfies the following:
Primary voltage = 120V @ 60Hz
V_DC = 12V
I_R2 = 100 mA (R2 being the load)
V_r(R2) <= .3V

Homework Equations

C=I_DC/(2fV_r)
I_DC=I_R3 + I_R1

The Attempt at a Solution

I tried calculating the capacitor, but how am I supposed to get I_DC if I don't have any other current?

 

[MATLABdude]

Remember that a reversed Zener diode clamps the voltage, but must be above the zener current (i_{zk}) in order to do so:
http://www.electronics-tutorials.ws/diode/diode_7.html