16-25(b+3) square emergency question. if you can, prove your intelligence and me with this problem. a lot!

Since 16 and 25 are perfect squares you can factor the first part.
4^2-5^2(b+3)^2
=(4-5(b+3))(4+5(b+3))
=(4-5b-15)(4+5b+15)
=(-11-5b)(19+5b)

Which can be expanded if necessary,
= -209+150b-25b^2