Licensing Netbackup 7.5 for cluster server

Hi,

I have 4 physical servers running on windows 2008 R2 enterprise edition. the first two servers are clustered running on Oracle ERP 12.1.3 (Load balancing) and the remaining two servers are also clustered and running on Oracle DB 11.2.3 (RAC ) with 2 cpu's

The backup server is Netbackup 7.5 enterprise server.

Does i need to purchase 4xApplication db licence + 4x Standard/enterprise client?

Please confirm?

Thanks