You are assigned to install two DS2246 shelves, three DS4243 shelves, and one DS4486 shelf.
How many rack units (U space) should you account for in this rack layout?

A.
6U

B.
20U

C.
10U

D.
22U

Explanation:
DS2246 rack units: 2U (Here: 2*2 -> 4U)
DS4243 rack units: 4U (Here: 3*4 -> 12U)
DS4286 rack units: 4U (Here: 1*4 -> 4U)
Total: 20U (4+12+4) NetApp Disk Shelves and Storage Media Technical Specifications
http://www.netapp.com/se/products/storage-systems/disk-shelves-and-storage-media/diskshelves-tech-specs.aspx