Answer:
c. Zhen spends 6 1/2 hours working per audiobook.
Step-by-step explanation:
The table below gives some completed audio lengths and the amount of time Zhen spends on the audiobook.

We observe that from the table, in 6.5 hours, Zhen completes 1 audiobook.
In fact, across the table:

Therefore, in this situation, 6.5 hours mean that Zhen spends 6.5 hours working per audiobook.
The correct option is C.