Case (i): When all bulbs are glowing, then,

Req=32R
Then, initially power consumption will be from the equation,
Power P=RE2
Pi=ReqE2=2R3E2...(1)
Case (ii): When two bulbs in section A and one bulb in the section are glowing,

Req′=2R+R=23R
Pf=Req′E2=3R2E2...(2)
From above two equations, ratio of power is,
PfPi=49