Students can practice finding the missing variable in these simple addition equations.

Let's solve each equation for $ x $. These are all simple linear equations of the form:

$$
a + x = b
$$

To solve for $ x $, we subtract $ a $ from both sides:

$$
x = b - a
$$

We'll go through each one step by step.

---

1. $ x + 38 = 63 $
$ x = 63 - 38 = 25 $

2. $ 34 + x = 55 $
$ x = 55 - 34 = 21 $

3. $ 16 + x = 29 $
$ x = 29 - 16 = 13 $

4. $ 20 + x = 39 $
$ x = 39 - 20 = 19 $

5. $ 18 + x = 32 $
$ x = 32 - 18 = 14 $

6. $ x + 12 = 28 $
$ x = 28 - 12 = 16 $

7. $ 16 + x = 19 $
$ x = 19 - 16 = 3 $

8. $ x + 38 = 43 $
$ x = 43 - 38 = 5 $

9. $ x + 9 = 38 $
$ x = 38 - 9 = 29 $

10. $ 4 + x = 22 $
$ x = 22 - 4 = 18 $

11. $ 32 + x = 63 $
$ x = 63 - 32 = 31 $

12. $ 15 + x = 51 $
$ x = 51 - 15 = 36 $

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Final Answers:

1. $ x = 25 $
2. $ x = 21 $
3. $ x = 13 $
4. $ x = 19 $
5. $ x = 14 $
6. $ x = 16 $
7. $ x = 3 $
8. $ x = 5 $
9. $ x = 29 $
10. $ x = 18 $
11. $ x = 31 $
12. $ x = 36 $

✔ All solved! Let me know if you'd like these written out in a formatted worksheet style.