6. The circuit shown below has three inputs $V_0$, $V_1$, and $I_0$. The output of this circuit is $v_{ab}$. The
output is related to the inputs by
$v_{ab} = aV_0 + bV_1 + cI_0$
where a, b, and c are constants.
(a) Explain the principle of superposition in electric circuits.
(b) Determine the values of a, b, and c if $R_1 = 1200\Omega$, $R_2 = 400\Omega$, and $R_3 = 30\Omega$.