Answer
Negative correlation
Work Step by Step
We determined the type of correlation between the year and the shipment of CDs and we have to determine the type of correlation between the shipment of cassettes and the shipment of CDs.
We know that when the year increases, the shipment of cassettes decreases, but we also know that when the year increases, the shipment of CDs increases, so when the shipment of cassettes increases, the shipment of CDs will decrease. The correlation between the shipment of cassettes and the shipment of CDs is $\textbf{negative}$.
The most important real-world factor which might account for this is the change in the market from cassette players to computers. A CD has an improved capacity of storing files of all types (audio, video, text).
