The switch positions in the figure apply when digital

Question

Programmable Voltage Divider

Given Figure shows a programmable voltage divider in which digital inputs b₀ and b₁ control complementary analog switches connecting a multitap voltage divider to the analog output v_O.

The switch positions in the figure apply when digital inputs are low. When inputs go high the switch positions reverse. Find the analog output voltage for (b₁,b₀) = (0,0), (0,1), (1,0), and (1,1) when V_REF = 12 V.