Answer:
years
Step-by-step explanation:
Period is:

The speed of the galaxy is 230 km/s. Its angular speed is given by:
Where R=25000 light years
Now, let N be the amount of seconds in 1 year.
This value will be in meters.
Replacing this value:


Now, the period will be:
This value is in seconds. Since we are asked to give the answer in years, we have to divide by N (amount of seconds in a year:

years