I'm relearning all my calculus after not using it for years. I'm starting fresh with limits and I have a limit question.

Please find the limit as s approaches a of (s^4 - a^4)\(s^2 - a^2). At first glance it looks like that when you plug in a to the s term then the limit is 0/0. However my book is saying the answer is 2a^2. How do they get to this answer?