The potential drop across the 3  Ω resistor is

Equivalent resistance, R=4+3 ×63 + 6 =6Ω  and main current  i=ER=36  =0.5 ANow potential difference across the combination of6 Ω  and  6 Ω,  V = 0.5 × 3 ×63 + 6 =1 VThe same potential difference also develops across 3 Ω resistance.