Hi Akanshalsat,
It seems like you understand the main ideas here. Tony told us that the newer videocassettes are economical for a rental store to stock. His reasoning is that even though the new kind don't last as long, they are much cheaper than the old kind.
Anna points out that the bulk of the cost of stocking videos, over half of the total cost, goes towards royalties. Anna seems to be arguing that there is not going to be a large decrease in price, since 95% of the cost in stocking videos would not change because of the new technology.
We want to weaken her argument by saying that it would make a significant difference in cost for a store to stock up on the new kind of cassettes.
Answer choice (C) tells us that along with the reduction in cost of the cassettes themselves, buying the new kind would lower the royalties paid to the studio. Since Anna just told us that this accounted for over half of the cost of stocking a videocassette, then it seems like stocking the new kind of cassettes would result in a significant cost reduction.
Let us know if you have any other questions!