\triangle R S T \cong \triangle A B C. \angle R S T = \angle C B A. S T = 2y - 8, and C B = y + 13. Find x.
Choices:
A:8
B:10
C:13
D:21
Please directly answer the question and provide the correct option letter, e.g., A, B, C, D.
Question: \triangle R S T \cong \triangle A B C. \angle R S T = \angle C B A. S T = 2y - 8, and C B = y + 13. Find x.
Choices:
A:8
B:10
C:13
D:21
Please first conduct reasoning, and then answer the question and provide the correct option letter, e.g., A, B, C, D, at the end.
Question: \triangle R S T \cong \triangle A B C. \angle R S T = \angle C B A. S T = 2y - 8, and C B = y + 13. Find x.
Choices:
A:8
B:10
C:13
D:21