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 \(\varphi_{3}=5 \mathrm{~V}\)