#### Answer

$g(f(x))=21x-62$

#### Work Step by Step

The student incorrectly omitted the expression $+8$ in his solution to get $g(f(x)).$
With $f(x)=
3x-10
$ and $g(x)=
7x+8
,$ then by replacing $x$ with $f(x)$ in $g,$
\begin{array}{l}\require{cancel}
g(f(x))=g(3x-10)
\\\\
g(f(x))=7(3x-10)+8
\\\\
g(f(x))=21x-70+8
\\\\
g(f(x))=21x-62
.\end{array}