In which of the following situations will a collaborative filtering system be the most appropriate learning algorithm to use?

$1.$ You run an online gift store and you have ratings from many users. You want to predict the expected sales volume i$.$e number of gifts sold as a function of the average rating of gifts.

$2.$ You manage a technical article website and you have ratings from many users. For each user, you want to recommend another article he$/$she will like based on his$/$her ratings and other users' ratings.