Answer:
Bulb will remain at constant brightness for 6 hour
Step-by-step explanation:
We have given resistance of the bulb R = 4 ohm
Potential difference of the battery V = 2 volt
So current

Capacity of the battery is given as 3 amp hour
We have to find the time by which bulb will remain at constant brightness
So time will be

So bulb will remain at constant brightness for 6 hour