Answer
$x=6$
Work Step by Step
Using the properties of equality, the value of $x$ in the given equation, $
c\cdot\dfrac{21}{a}=\dfrac{7cx}{2a}
$, is
\begin{array}{l}\require{cancel}
\dfrac{2a}{7c}\cdot\dfrac{21c}{a}=\dfrac{7cx}{2a}\cdot\dfrac{2a}{7c}
\\\\
\dfrac{2\cancel{a}}{\cancel{7c}}\cdot\dfrac{\cancel{7c}\cdot3}{\cancel{a}}=\dfrac{14acx}{14ac}
\\\\
6=x
\\\\
x=6
.\end{array}
