Answer
$\text{a) }
f(g(x))=2.4276x+6.7732
\\\\\text{b) }
g(f(x))=2.4276x+14.9152$
Work Step by Step
$\bf{\text{Solution Outline:}}$
With
\begin{array}{l}\require{cancel}
f(x)=
0.68x+2.36
\\g(x)=
3.57x+6.49
,\end{array}
replace $x$ with $g(x)$ in $f$ to find $f(g(x)).$ To find $g(f(x)),$ replace $x$ with $f(x)$ in $g.$
$\bf{\text{Solution Details:}}$
Replacing $x$ with $g(x)$ in $f,$ then
\begin{array}{l}\require{cancel}
f(g(x))=f( 3.57x+6.49 )
\\\\
f(g(x))=0.68(3.57x+6.49)+2.36
\\\\
f(g(x))=2.4276x+4.4132+2.36
\\\\
f(g(x))=2.4276x+6.7732
.\end{array}
Replacing $x$ with $f(x)$ in $g.$ Hence,
\begin{array}{l}\require{cancel}
g(f(x))=g(0.68x+2.36)
\\\\
g(f(x))=3.57(0.68x+2.36)+6.49
\\\\
g(f(x))=2.4276x+8.4252+6.49
\\\\
g(f(x))=2.4276x+14.9152
.\end{array}
Hence,
\begin{array}{l}\require{cancel}
\text{a) }
f(g(x))=2.4276x+6.7732
\\\\\text{b) }
g(f(x))=2.4276x+14.9152
.\end{array}
