1. **State the problem:** We need to find the cost per person when the total bill for nine people is 135. 2. **Formula used:** To find the cost per person, divide the total bill by the number of people. $$\text{Cost per person} = \frac{\text{Total bill}}{\text{Number of people}}$$ 3. **Substitute the values:** $$\text{Cost per person} = \frac{135}{9}$$ 4. **Simplify the fraction:** $$\text{Cost per person} = \frac{\cancel{135}}{\cancel{9}} = 15$$ 5. **Answer:** The cost per person is 15.