Given,
The number of paper clips used for 9 cm paper is 3.
Consider, the number of paper clips used for 15 cm paper,
By proportionality,
[tex]\begin{gathered} \frac{3}{9}=\frac{x}{15} \\ 3\times15=9\times x \\ \frac{45}{9}=x \\ x=5 \end{gathered}[/tex]Hence, the number of paper clips used for 15 cm of paper is equal to 5.