Math
posted by Mary .
How do I set this up and solve it?
Tom has a collection of 30 CDs and Nita has a collection of 15 CDs. Tom is adding 1 CD a month to his collection while Nita is adding 4 CDs a month to her collection. Find the number of months after which they will have the same number of CDs.

Tom 30 + n
Nita 15 + 4 n
30 + n = 15 + 4 n
15 = 3 n
n = 5