Answer :
we can find a ratio to calculate the relation between the numbers
[tex]\frac{6}{4}=\frac{3}{2}[/tex][tex]\frac{15}{10}=\frac{3}{2}[/tex][tex]\frac{18}{12}=\frac{3}{2}[/tex]now, keeping the ratio
[tex]\frac{x}{18}=\frac{3}{2}[/tex]and solve x
[tex]\begin{gathered} \frac{x}{18}=\frac{3}{2} \\ x=\frac{3\times18}{2} \\ x=27 \end{gathered}[/tex]needed 27 cups of sugar to 18 cups of water