A real Zener diode has a dynamic resistance rz = 4.0 Ω in breakdown…

Step 1. The parallel resistance. $r = \dfrac{r_z R_L}{r_z + R_L} = \dfrac{4.0\ \Omega \times 1000\ \Omega}{1004\ \Omega} = 3.98\ \Omega$.

Step 2. The divider. $\Delta V_{out} = \Delta V_{in}\,\dfrac{r}{R_s + r} = 3.0\ \text{V} \times \dfrac{3.98\ \Omega}{120\ \Omega + 3.98\ \Omega} = 0.0964\ \text{V} = 96.4$ mV.

Step 3. The percentage. $\dfrac{0.0964\ \text{V}}{6.8\ \text{V}} \times 100 = 1.42\ \%$.