I got a problem of this circuit diagram, where a and b are open circuit

I need to find the voltage across R4 but i feel confused with finding equivalent resistance

Here my way:

R1 || R2 and R3

R2 is in series with R3

R2 || R4

therefore:

1/R2 + 1/R4 = 0.1= 10k ohms

10k + R3 = 10k + 20k = 30k ohms

1/10k + 1/30k = 7.5k ohms

by V=IR

I=4/7.5k=5.3333x10^-4

the voltage across R4=(5.33x10^-4 )(20k)=10.667V

am i correct in this way since i dont have the answer