How do i find the 25th term of the arithmetic sequence -39, -31, -23, -

Every time you subtract 8 to get to the next number. So just multiply 8x25 to get 200 and then add 200 instead of subtract (because it's a negative number) to -15 and you get the 25th number, which is 185.

The method to find the female dormitory is 2-d=800