What is the meaning of a small o in between function names? i.e (f o g) I am helping with homework.  
I am stumped here - What is the meaning of the small round circle, or small "o" in question 19 (that I underlined) and question 20


It is function composition. If you have one function $f(x)$, and another function $g(x)$, then we can create a new function named  $g\circ f$ (read as: "$g$ composed with $f$") that is defined as
$$(g\circ f)(x)=g(f(x))$$
For example, if $f(x)=x+1$, and $g(x)=2x-1$, then
$$(g\circ f)(x)=g(f(x))=g(x+1)=2(x+1)-1=2x+1$$
