Answer
$\left[ 3,5 \right]$
Work Step by Step
Solving the inequalities separately, then,
\begin{array}{l}
-7x\le-21\\
x\ge3
,\\\\\text{and}\\\\
x-20\le-15\\
x\le5
.\end{array}
Using the conjunction "and", then the solution set is the set common to both inequalities. Hence, the solution set is $
\left[ 3,5 \right]
$.
