Answer :
next 3 steps:
ABCDCBA
ABCDEDCBA
ABCDEFEDCBA
Patern: add 2 letters
1. 1
2. 3
3. 5
4. 7
5. 9
6. 11
7. 13
8. 15
9. 17
10. 19
The 10th step has 19 letters
next 3 steps:
ABCDCBA
ABCDEDCBA
ABCDEFEDCBA
Patern: add 2 letters
1. 1
2. 3
3. 5
4. 7
5. 9
6. 11
7. 13
8. 15
9. 17
10. 19
The 10th step has 19 letters