College Algebra 7th Edition

$\displaystyle \frac{25}{3+x}$
To get the concentration, we divide the amount of salt (25 oz) by the volume of the mixture. The total volume will be the sum of the 3 gallons of brine and $x$ gallons of water: $3+x$ Thus the concentration is: $\displaystyle \frac{25}{3+x}$