In the given circuit voltage across R₄ is:

0.4 V

Here $\left(R_3\right) 60 \Omega$ and $\left(R_4\right) 30 \Omega$ are in parallel. Their combination is in series with $\left(R_5\right) 30 \Omega$ resistance. Their effective resistance is $=\frac{60 \times 30}{60+30}+30 \Omega=20+30=50 \Omega$

It is in parallel with resistance $\left(R_2\right) 50 \Omega$ with together is in series with $\left(R_1\right) 50 \Omega$. The effective resistance of the circuit is $=50+\frac{50 \times 50}{50+50}=50+25=75 \Omega$

Current in the circuit is $I=\frac{3 V}{75 \Omega}=\frac{1}{25} \mathrm{~A}$

Current through $R_5=\frac{1}{2} \times \frac{1}{25}=\frac{1}{50} \mathrm{~A}$

Current through $R_4=\frac{2}{3} \times \frac{1}{50}=\frac{1}{75} \mathrm{~A}$

Potential difference across $R_4=30 \times \frac{1}{75}=0.4 V$