Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is: 
Definitions:
Structuralism
A theoretical paradigm in the humanities and social sciences that emphasizes the understanding of cultural and social phenomena in terms of the relationships and structures that shape them.
Oceanic Trench
Deep, elongated depressions in the ocean floor formed by the subduction of a tectonic plate under another.
Mid-Ocean Ridge
An underwater mountain range, formed by plate tectonics, that encircles the globe along the ocean floor.
Island Arc
A curved chain of volcanic islands located at a tectonic plate margin, above a subducting zone.
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