4 liters are proportional to 2 days.
To find how many days are proportional to 18 liters, we can use the next proportion:
[tex]\frac{4\text{ liters}}{18\text{ liters}}=\frac{2\text{ days}}{x\text{ days}}[/tex]Solving for x:
[tex]\begin{gathered} 4\cdot x=2\cdot18 \\ x=\frac{36}{4} \\ x=9 \end{gathered}[/tex]Reid needs 9 days to jar 18 liters of jam.
