3630欧,过程如下,不明可追问设电烙铁的电阻为R由P=U^2/R得40=220*220/R电烙铁的电阻R=1210欧接a时,P1=U^2/1210接b时,P2=U^2/(1210+RL)因为P1=4P2,所以U^2/1210=4U^2/(1210+RL)解之有灯的电阻RL=3630欧
