The formula for current is:
i = v / R (* i=current, v=voltage, R=resistance)
So for part A, we are given E as the voltage, and the lightbulb with resistance R.
Total current in a circuit remains the constant, so we get that:
IA = E/R
but for IB and IC since we have to lightbulbs we divide each current by 2 and get:
IB = E/2R
IC = E/2R
since they both have the same current and voltage they will also have the same brightness, so
B = C
A will be brighter then B and C because it has more current going through it, and the same amount of voltage, therefore it has greater power and will be brighter.
A > B = C