The reverse breakdown voltage of a Zener diode is 5.6 V in the given circuit.

The current IZ through the Zener is :
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9 = Vz + VR1
Vz = 5.6 V
VR1 = 9 – 5.6
VR1 = 3.4
V2= VR2 = IR2 (R2)
Iz = (17 – 7)mA = 10 mA