Because Earth's rotation is gradually slowing, the length of each day increases: The day at the end of 1.0 century is 1.0 ms longer than the day at the start of the century. In 27 centuries, what is the total (in hours) of the daily increases in time (that is, the sum of the gain on the first day, the gain on the second day, etc.)?

I tried to use the sum of arithmetic sequences:

I converted 27 centuries to days to use as n. I am not sure what I should use as d though. I tried converting 1ms/century into .000027ms/day and used that as d.

My formula was:

S985,500={(985,500)[(2+985,499)(.000027)]}/2

Overall, I got 3.97 hours as the total of the daily increases but it was incorrect.

What method should I use to get my result?