first off, let's convert the mixed fraction to "improper", and then check,
[tex] \bf \stackrel{mixed}{124\frac{7}{8}}\implies \cfrac{124\cdot 8+7}{8}\implies \stackrel{improper}{\cfrac{999}{8}}\\\\
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\begin{array}{ccll}
\stackrel{water}{gallons}&minutes\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
\frac{999}{8}&25\\\\
x&1
\end{array}\implies \cfrac{\quad \frac{999}{8}\quad }{x}=\cfrac{25}{1}\implies \cfrac{\quad \frac{999}{8}\quad }{\frac{x}{1}}=25 [/tex]
[tex] \bf \cfrac{999}{8}\cdot \cfrac{1}{x}=25\implies \cfrac{999}{8x}=25\implies 999=200x
\\\\\\
\cfrac{999}{200}=x\implies \stackrel{gallons}{4\frac{199}{200}}=x [/tex]
