Answer
$-\dfrac{7}{8}$
Work Step by Step
The given expression, $
\dfrac{7x-21}{24-8x}
,$ simplifies to
\begin{array}{l}\require{cancel}
\dfrac{7(x-3)}{8(3-x)}
\\\\=
\dfrac{7(x-3)}{-8(x-3)}
\\\\=
\dfrac{7(\cancel{x-3})}{-8(\cancel{x-3})}
\\\\=
\dfrac{7}{-8}
\\\\=
-\dfrac{7}{8}
.\end{array}
