1. **State the problem:** Mo reads $\frac{3}{4}$ of a book each week. We want to find out how many books he has read after 12 weeks. 2. **Formula used:** Total books read = (books read per week) $\times$ (number of weeks) 3. **Apply the values:** $$\text{Total books} = \frac{3}{4} \times 12$$ 4. **Calculate:** $$\frac{3}{4} \times 12 = \frac{3 \times 12}{4} = \frac{36}{4} = 9$$ 5. **Interpretation:** After 12 weeks, Mo has read 9 books. **Final answer:** Mo has read **9** books after 12 weeks.