Answer :
[tex]\dfrac{1}{x}+\dfrac{1}{12}=\dfrac{1}{8\dfrac{4}{7}}\\
\dfrac{1}{x}=\dfrac{1}{\dfrac{60}{7}}-\dfrac{1}{12}\\
\dfrac{1}{x}=\dfrac{7}{60}-\dfrac{1}{12}\\
\dfrac{1}{x}=\dfrac{7}{60}-\dfrac{5}{60}\\
\dfrac{1}{x}=\dfrac{2}{60}\\
\dfrac{1}{x}=\dfrac{1}{30}\\
x=30
[/tex]
30 hrs
30 hrs