How much room (in inches) is required for this server?

A new 4U server is being installed in an existing server rack. How much room (in inches) is
required for this server?

A.
7 inches (17.9 cm)

B.
6 inches (15.3 cm)

C.
4 inches (10.2 cm)

D.
8 inches (20.4 cm)