Which version of Zend Server for IBM i do I have?

Here is the easiest way to learn the version of Zend Server installed on an IBM i system.
[Updated December 20, 2017]

From a 5250 command line, follow these four steps:

1. GO LICPGM
2. Take option 10 (Display installed licensed programs)
3. Scroll down to the licensed program 2ZSVRPI, 6ZSVRPI, or 7PHPZND 
     (on my system, it's the last entry)
4. Read the product description,
     containing version numbers for Zend Server and PHP,
     in the form "Zend Server for IBM i [version] ( PHP [version])"

On my IBM i, I see:
7PHPZND   *INSTALLED   Zend Server for IBM i 9.1.2 ( PHP 7.1 )
so Zend Server is at 9.1.2 and PHP is 7.1.

Thanks to Zend’s Sam Pinkhasov for this tip.