Evaluate, where f(x)=(x-4)^2-1

Question

when f(a-5)

How would i solve this?
This is what i got so far.
f(a-5)=[(a-5)-4]^2 -1
=(a-9)^2 -1

Answer 1

You are on the right track, now do the (a-9)(a-9) and subtract 1

Answer 2

(a+9)(a+9)-1

then i don't know what to do.

Answer 3

Would it be;
a^2-9a-9a+81
a^2-18a+81-1
a^2-18a+80