We need 3 cups of spinach for each 1/2 cup of pecans.
Then we have:
[tex]\begin{gathered} \frac{2\text{ cups of spinach}}{3\text{ cups of spinach}}=\frac{x\text{ cups of pecans}}{\frac{1}{2}\text{ cups of pecans}} \\ \frac{x}{\frac{1}{2}}=\frac{2}{3} \\ x=\frac{1}{2}\cdot\frac{2}{3} \\ x=\frac{1}{3} \end{gathered}[/tex]Answer: It will be needed 1/3 cup of pecans