Sometimes you will experience that feature installation in windows server 2012 fails commonly on .Net 3.5.
this is because this installation refers to source files which includes in Server 2012 media. by giving the path to SXS folder manually of your media on Confirmation window in Feature installation wizard resolves this as figured below.
Insert media and Click on “Specify alternate source path” and provide location of SXS folder within Server 2012 Media – E:\sources\sxs
Now the setup can find the files and the installation would be success.