i cant seem to get one of these answers when i work it out. please help

Answer:
first option
Step-by-step explanation:
To obtain ( f ○ g)(x) substitute x = g(x) into f(x) , that is
f([tex]\frac{1}{2x}[/tex] )
= [tex]\frac{2}{\frac{1}{2x}+3 }[/tex] ( multiply numerator/ denominator by 2x to clear the fraction
= [tex]\frac{2(2x)}{2x(\frac{1}{2x}+3) }[/tex]
= [tex]\frac{4x}{1+6x}[/tex]