Problem 3.185

Find the current flowing through the resistance $R_{1}$ of the circuit shown in Fig. 3.48 if the resistances are equal to $R_{1}=10 \Omega$, $R_{2}=20 \Omega,$ and $R_{3}=30 \Omega_{4}$ and the potentials of points $1,2,$ and 3 are equal to $\varphi_{1}=10 \mathrm{~V}, \varphi_{2}=6 \mathrm{~V},$ and $\varphi_{3}=5 \mathrm{~V}$