Which of these three systems need its RAM to be upgraded and why

These are the images of 'Memory' section of Resource Monitor for 3 systems; The two with 8GB RAM have core i7 cpu while the one with 4GB of RAM has core i5 cpu; Based on these graphs which of these systems needs (or can be benefited) by adding more RAM?

Update 1: The system with 8GB RAM (3768MB Free) is mostly used for playing movies and web browsing; The other systems (8GB and 4GB RAM) are used for heavy visualization (multiple VMs) and feature rich graphic applications such Photoshop and Illustrator;

Please say Why and how you can tell;

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