well, if 6/7 is 18, and how many is the 7/7 or a 1 whole(total)?
[tex]\bf \begin{array}{ccll}
\stackrel{frational}{amount}&\stackrel{quantity}{amount}\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
\frac{6}{7}&18\\\\
\frac{7}{7}&x
\end{array}\implies \cfrac{\frac{6}{7}}{\frac{7}{7}}=\cfrac{18}{x}\implies \cfrac{\frac{6}{7}}{1}=\cfrac{18}{x}\implies \cfrac{6}{7}=\cfrac{18}{x}
\\\\\\
x=\cfrac{7\cdot 18}{6}[/tex]
