#### Answer

$f\left( \dfrac{1}{3} \right)=0$

#### Work Step by Step

Substituting $x=\dfrac{1}{3}$ in $f(x)=3x-1,$ then
\begin{array}{l}\require{cancel}
f(x)=3x-1
\\\\
f\left( \dfrac{1}{3} \right)=3\left( \dfrac{1}{3} \right)-1
\\\\
f\left( \dfrac{1}{3} \right)=1-1
\\\\
f\left( \dfrac{1}{3} \right)=0
.\end{array}