1. **Stating the problem:** We are given a proportional relationship between pens and copies: 3 pens = 5 copies. We want to find how many copies correspond to 9 pens. 2. **Formula and rules:** If 3 pens correspond to 5 copies, then 1 pen corresponds to $\frac{5}{3}$ copies by dividing both sides by 3. 3. **Intermediate work:** To find the number of copies for 9 pens, multiply 9 pens by $\frac{5}{3}$ copies per pen: $$9 \times \frac{5}{3} = \frac{45}{3} = 15$$ 4. **Explanation:** Since 1 pen equals $\frac{5}{3}$ copies, multiplying by 9 pens gives the total copies as 15. 5. **Final answer:** 9 pens correspond to **15 copies**.