Three girls are being loud and going crazy in a restaurant while one girl watches annoyed.
Three girls and a friend are eating at a restaurant
That another girl watches the first three girls implies she is related in some way, such as being a friend. If the three girls are said to be acting a certain way in a restaurant, while the friend watches, then they all can be said to be in a restaurant. Restaurants are a place to eat food, so they all can be said to be eating at a restaurant.
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