Apple Physical Design Engineer interview questions

the interviewer gave me scheme of two blocks, in the left block (block A) there were 2 FF, FFa and FFb. in block B there were only logic. FFa routed through logic to block B, and returned through logic to FFb in Block A. the interviewer tell me that is 150ns delay in the timing path between FFa and FFb, and ask me to describe what can be the cause and how to fix it.