Add four-digit numbers with regrouping

Every one needs regrouping.

1. 1,408 + 1,052 =
2. 1,117 + 1,048 =
3. 1,207 + 1,143 =
4. 1,450 + 1,483 =
5. 1,786 + 1,435 =
6. 1,875 + 1,908 =
7. 1,035 + 1,984 =
8. 1,757 + 1,742 =
9. 2,999 + 2,240 =
10. 1,339 + 2,109 =
11. 1,880 + 1,898 =
12. 1,366 + 2,225 =
13. 2,609 + 1,767 =
14. 1,495 + 1,052 =
15. 3,217 + 3,983 =
16. 1,479 + 1,096 =
17. 2,778 + 2,131 =
18. 4,886 + 3,420 =
19. 1,146 + 2,044 =
20. 1,634 + 1,919 =