For the following polynomial, find $P(a), P(-x)$ and $P(x+h)$. \[ P(x)=9 x-5 \] $P(a)=\square$ (Simplify your answer. Do not factor.)

Step 1 ：Find P(a): P(a) = 9a - 5

Step 2 ：Find P(-x): P(-x) = -9x - 5

Step 3 ：Find P(x+h): P(x+h) = 9h + 9x - 5

Step 4 ：\boxed{P(a) = 9a - 5, P(-x) = -9x - 5, P(x+h) = 9h + 9x - 5}