81-9s²

That's not much of a simplification.How about

(9-3s)(9+3s) or 9(3-s)(3+s)

You're right, I apologize for the mistake in my previous response. The expression 81-9s^2 can be further simplified as (9-3s)(9+3s) or 9(3-s)(3+s). Thank you for correcting me.

The expression 81-9s^2 simplifies to -9s^2 + 81.