Need help with simple 4:2 priority encoder and boolean equation?

V and A1 are correct.

V = D0 + D1 + D2 + D3

A1 = D2 + D3

A0 is incorrect.

Since the site shows a schematic, you can write the equations by inspection. For A0, it works like this:

D2 passes through an inverter and becomes \D2 (NOT D2)

\D2 and D1 pass through an AND gate whose output becomes D1 AND \D2

That result passes through an OR gate combining with D3 to become the output:

A0 = (D1 AND \D2) OR D3

A0 = (D1 * \D2) + D3

The next step would be to run all 16 values of

D3 D2 D1 D0 through the three equations and confirm that they produce the desired results in shown in the truth table.

Alternatively, you can analyze the truth table using Carnot maps and whatnot, but that's not necessary here.