1. **Problem statement:** We want to find a way to make the number 12 using the numbers 7, 9, 13, and 20. 2. **Approach:** We can try to express 12 as a combination of these numbers using addition or subtraction. 3. **Check simple combinations:** - 7 + 9 = 16 (too high) - 13 - 7 = 6 (too low) - 20 - 9 = 11 (close but not 12) 4. **Try combining more than two numbers:** - 20 - 9 - 7 = 4 (too low) - 13 - 9 + 7 = 11 (close) 5. **Try multiplication or division if allowed:** - 7 + (13 - 9) = 7 + 4 = 11 (close) 6. **Try subtraction and addition:** - 20 - 7 - 1 = 12 but 1 is not in the list 7. **Try using multiples:** - 9 + 7 - 4 = 12 but 4 is not in the list 8. **Conclusion:** Using only 7, 9, 13, and 20 with addition and subtraction, 12 cannot be formed exactly without introducing other numbers or operations. **Final answer:** It is not possible to make 12 exactly using only 7, 9, 13, and 20 with basic addition and subtraction.