1. **State the problem:** We need to find what percentage of 6th grade students have returned their signed permission forms. 2. **Identify the total number of students:** The total number of students is the sum of those who have returned forms and those who have not. $$\text{Total students} = 108 + 42 = 150$$ 3. **Formula for percentage:** $$\text{Percentage} = \left(\frac{\text{Part}}{\text{Whole}}\right) \times 100$$ 4. **Apply the formula:** $$\text{Percentage returned} = \left(\frac{108}{150}\right) \times 100$$ 5. **Simplify the fraction:** $$\frac{108}{150} = \frac{\cancel{108}}{\cancel{150}} = \frac{36}{50}$$ 6. **Calculate the percentage:** $$\frac{36}{50} \times 100 = 0.72 \times 100 = 72$$ 7. **Final answer:** **72%** of the 6th grade students have returned their signed permission forms.