Help with composite functions? Suppose that $u$ and $w$ are defined as follows: 
$u(x) = x^2 + 9$
$w(x) = \sqrt{x + 8}$
What is: 
$(u \circ w)(8) = $
$(w \circ u)(8) = $
I missed this in math class. Any help?

$(u\circ w)$ is the composition of function $u$ over $w$.  
It means: apply function $u$ to the result applying function $w$.  That is all.
$$(u\circ w)(x) = u(w(x))$$
And conversely: $(w\circ u)(x) = w(u(x))$
