From the circuit shown below, the maximum and minimum values of Zener diode current are 

The Zener diode acts as the voltage regulator in the circuit and the voltage supply is variable hence, excess of voltage over 50 V will be across 5KΩ resistance.

Thus, minimum voltage across 5KΩ resistance is 80 V−50 V=30 V

Current through 5KΩ resistance is given by $\frac{30}{5\times {10}^3}=6\mathrm{mA}.$

The current through the 10KΩ resistance is given by $\frac{50}{10\times {10}^3}=5\mathrm{mA}.$

Hence the minimum current through the Zener diode is 1mA.

Maximum voltage across 5KΩ resistance is 120 V−50 V=70 V

Current through 5KΩ resistance is given by $\frac{70}{5\times {10}^3}=14\mathrm{mA}.$

The current through the 10KΩ resistance is given by $\frac{50}{10\times {10}^3}=5\mathrm{mA}.$

Hence the maximum current through the Zener diode is 9mA.