The value of the resistor , $R_s$, needed in the dc voltage regular circuit shown here, equals :

Question

$\begin{array}{1 1} (V_i-V_L)/nI_L \\ (V_i+V_L)/nI_L \\ (V_i-V_L)/(n+1)I_L \\ (V_i+V_L ) /(n+1)I_L \end{array} $