To solve the exercise you can use the rule of three, like this
[tex]\begin{gathered} 1.5\text{ quarts}\rightarrow100\text{ \% }\Rightarrow\text{ Green paint} \\ x\text{ quarts}\rightarrow30\text{ \%}\Rightarrow\text{ Yellow paint} \end{gathered}[/tex][tex]\begin{gathered} x=\frac{30\text{ \% }\ast\text{ 1.5 quarts}}{100\text{ \%}} \\ x=0.45\text{ quarts} \end{gathered}[/tex]
Therefore, Curt and Melanie should use 0.45 quarts of yellow paint to make seafoam green paint.
