Students substitute the values x=8 and y=4 to solve these 20 pre-algebra problems.

We are given that x = 8 and y = 4.
We need to plug these values into each expression and calculate the result.

Let’s go one by one:

1. x + y → 8 + 4 = 12
2. 2 + x - y → 2 + 8 - 4 = 10 - 4 = 6
3. 12 + y - x → 12 + 4 - 8 = 16 - 8 = 8
4. x - 6 → 8 - 6 = 2
5. x + y - 6 → 8 + 4 - 6 = 12 - 6 = 6
6. 17 + x - y → 17 + 8 - 4 = 25 - 4 = 21
7. x + y + 3 → 8 + 4 + 3 = 12 + 3 = 15
8. x - 3 + 8 → 8 - 3 + 8 = 5 + 8 = 13
9. y - 2 + 4 → 4 - 2 + 4 = 2 + 4 = 6
10. x - y → 8 - 4 = 4

Now the second column:

11. 8 - x + y → 8 - 8 + 4 = 0 + 4 = 4
12. 14 - y → 14 - 4 = 10
13. x - y + 6 → 8 - 4 + 6 = 4 + 6 = 10
14. y - 1 + x → 4 - 1 + 8 = 3 + 8 = 11
15. x - 2 - y → 8 - 2 - 4 = 6 - 4 = 2
16. y + 15 - 3 → 4 + 15 - 3 = 19 - 3 = 16
17. 12 - (x + y) → First, x + y = 8 + 4 = 12 → 12 - 12 = 0
18. x - y - 3 → 8 - 4 - 3 = 4 - 3 = 1
19. 11 - x + y → 11 - 8 + 4 = 3 + 4 = 7
20. x - y - 2 → 8 - 4 - 2 = 4 - 2 = 2

All calculations checked — no mistakes found.

Final Answer:
1. 12
2. 6
3. 8
4. 2
5. 6
6. 21
7. 15
8. 13
9. 6
10. 4
11. 4
12. 10
13. 10
14. 11
15. 2
16. 16
17. 0
18. 1
19. 7
20. 2