Use the function $f(x)=ln(x^2+16)$ to find the following. $($Round answers to two decimal places.$)$

a$.$ The domain of $f(x).$

$x^2+16>0,(-,)$

b$.$ The intervals where the function is increasing or decreasing.

c$.$ Any relative extrema $($ordered pairs $-$ tell if they are min or max$).$

d$.$ The intervals where the function is concave up or concave down.

e$.$ Any inflection points $($ordered pairs$).$