Answer:
6 months
Explanation:
Let the total chargers be y
and let the monthly charge be x
Apartment A
y=200+400x----------1
Apartment B
y=500+350x---------2
Equating 1 and 2 to solve for x we have
200+400x=500+350x
collecting like terms
200-500=350x-400x
-300=-50x
x=300/50
x=6