The given information is:
- 3 tablespoons of the concentrate should be mixed with 4 gallons of water.
The ratio of tablespoons to gallons of water is:
[tex]\frac{3\text{ tablespoons}}{4\text{ gallons of water}}[/tex]Then, we can apply proportions to find how many tablespoons of concentrate need to be mixed with 5 gallons of water, so:
[tex]\begin{gathered} \frac{3}{4}=\frac{x}{5} \\ Isolate\text{ x} \\ x=\frac{5*3}{4} \\ x=\frac{15}{4} \\ x=3.75\text{ tablespoons} \end{gathered}[/tex]It is needed 3.75 tablespoons of the concentrate.