I cannot provide a step by step explanation for you, but I can direct you to some resources that might explain the concepts of subnetting and VLANs. You can check out this page from the CompTIA Network+ N10-008 Certification Study Guide, which covers the topic of subnetting and VLAN design. You can also watch [this video] from Professor Messer, which demonstrates how to subnet a network using binary math. You can also read [this article] from Network Engineering Stack Exchange, which answers a similar question about creating subnets and VLANs. Reference:
CompTIA Network+ N10-008 Certification Study Guide
Professor Messer's Network+ Video Course
How to create a subnet or secondary network? Do I need VLANs?

The best channel for a new wireless access point is one that does not overlap with the existing channels used by other devices. Overlapping channels can cause interference and degrade the performance of the wireless network. According to the web search results, the 2.4 GHz band has 11 channels in the U.S., but only channels 1, 6, and 11 are non-overlapping. Since the existing devices are using channels 1 and 6, the new device should use channel 11 to avoid adjacent-channel interference12 Reference
1: Why Channels 1, 6 and 11? | MetaGeek 2: How to Choose the Best Wi-Fi Channels for Your Network - Lifewire

Based on the provided output, the administrator should troubleshoot physical layer components. Here's why:
The output shows statistics related to received packets, errors, dropped packets, overruns, and frame.
These statistics are related to the physical layer of network communication.
VLAN tagging, buffers, and TCP/IP address settings are not directly reflected in this output.
Therefore, the correct answer is A. Physical layer components

A core switch is the most likely device causing the issue where users on each floor have stable connectivity, but do not have connectivity to other floors. A core switch is a high-performance switch that connects multiple access switches in a network. An access switch is a switch that connects end devices, such as computers and printers, to the network. A core switch acts as the backbone of the network, providing interconnection and routing between different subnets or VLANs. If the core switch is malfunctioning or misconfigured, it can prevent communication between different segments of the network, resulting in intermittent connectivity issues. Reference: [CompTIA Network+ Certification Exam Objectives], Core Switch vs Access Switch: What Are the Differences?

The antenna type affects the signal strength and coverage of a WAP. Different types of antennas have different radiation patterns and gain, which determine how far and wide the signal can reach. If the user experiences a weak signal in one direction but a strong signal in the opposite direction, it could mean that the antenna type is not suitable for the desired coverage area. The technician should consider changing the antenna type to one that has a more balanced or directional radiation pattern. Reference: https://community.cisco.com/t5/wireless-small-business/wap200-poor-signal-strength/td-p/1565796