1U stands for one unit and it is a standard unit of measurement for rack-mounted servers. It is equal to 1.75 inches (4.45 cm) in height. A 42U rack can accommodate 42 1U servers or a combination of servers with different unit sizes. Therefore, the unit size per server should be 1U if there are 19 1U servers in a 42U rack. Reference: https://www.comptia.org/training/resources/exam-objectives/comptia-server-sk0-005-exam-objectives (Objective 1.2)

The first thing that the administrator should check is the network cable. The network cable is a physical medium that connects a server to a switch or other network device. The network cable can affect the speed and quality of the network connection, depending on its type, length, and condition. If the network cable is damaged, faulty, or incompatible, it can cause the server to connect at a lower speed than expected. Therefore, the administrator should check the network cable for any signs of wear, tear, or mismatch, and replace it if necessary.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 2, Lesson 2.1, Objective 2.1

The first action that the administrator should take before swapping out the GPU card inside a server is to shut down the server. This is to ensure that the server is not running any processes that might be using the GPU card, and to prevent any damage to the hardware or data loss due to sudden power loss. Shutting down the server also reduces the risk of electrostatic discharge (ESD) that might harm the components. Reference:
https://pcgearhead.com/installing-a-new-gpu/

The most likely cause of this issue is that the UEFI boot was interrupted by a missing Linux boot file, such as grub.cfg or vmlinuz, which are essential for loading the Linux kernel and booting the system. The £s> prompt indicates that the system entered into UEFI Shell mode, which is a command-line interface for troubleshooting UEFI boot issues. The administrator can use UEFI Shell commands to locate and restore the missing boot file or change the boot order. Verified References: [UEFI Shell Guide]