
To fix the above issue you need to perform following steps:
- Mount the OS to any drive on the server where you are trying to install SQL.
- Run the following command using administrator privileges
dism /online /enable-feature /featurename:NetFx3 /all /source:d:\sources\sxs

Where you need to replace d:\ with your OS mount drive.
3. After Enabling feature successfully , start the SQL Server 2014 setup again. Now you can install SQL 2014 with out any NetFx3 issue.