Answer
\[\left( g\circ f \right)\left( 0 \right)=-21\]
Work Step by Step
The value of the given composite function can be obtained using the definition of composite functions and the values of $f$ and $g$ at the required points.
Now, $f\left( 0 \right)=2\left( 0 \right)-5=-5$ , thus we have
$\begin{align}
& \left( g\circ f \right)\left( 0 \right)=g\left( f\left( 0 \right) \right) \\
& =g\left( -5 \right) \\
& =4\left( -5 \right)-1 \\
& =-21
\end{align}$
