Answer
$C=25$
Work Step by Step
Substituting $F=77$in the given equation, $
F=\dfrac{9}{5}C+32
,$ we obtain:
\begin{array}{l}\require{cancel}
77=\dfrac{9}{5}C+32
\\\\
77-32=\dfrac{9}{5}C
\\\\
45=\dfrac{9}{5}C
\\\\
\dfrac{5}{9}\cdot45=\dfrac{9}{5}C\cdot\dfrac{5}{9}
\\\\
\dfrac{5}{\cancel{9}}\cdot\cancel{9}(5)=C
\\\\
C=25
.\end{array}
