Find f(x) such that h(x) = f∘g(x), where g(x)=8x+4, and
      ____
h(x)=Ö8x+4.

f∘g(x) means to take the whole right side of the 
equation for g(x), and substitute that whole
expression for x in the right side of f(x).

So the question is: 

What would the right side of f(x) have to be so that
if we substituted the whole right side of g(x), which 
is 8x+4, for x in the right side of f(x) we would get
 ____
Ö8x+4  ???

If we think about it, the right side of f(x) would have
to be 
 _
Öx

in order that if we substituted 8x+4 for x we would get
 ____
Ö8x+4  

So therefore we'd have to have
        _
f(x) = Öx

Edwin