To identify why a user is unable to log in to Salesforce, the administrator should review the login history for the user. The login history shows the date and time of each login attempt, the source IP address, the browser and platform used, the login type (such as username and password or single sign-on), and the status (such as success or failure). The login history can help troubleshoot common login issues such as incorrect username or password, invalid security token, IP restrictions, or login hours violations. Checking the attempted logins by running the setup audit trail, pulling the password history, or resetting the security token for the profile will not help identify why a user is unable to log in. References: https://help.salesforce.com/s/articleView?id=sf.
monitoring_login_history.htm&type=5

To show a component that shows LinkedIn data only to sales users when they are on their mobile phones, the administrator should filter the component visibility with two conditions:
* User > Profile > name = sales User, which checks if the user's profile name is "sales User"
* Form Factor = phone, which checks if the user's device is a phone Filtering with view or role will not achieve the desired result. References: https://help.salesforce.com/s/articleView?id=sf.
app_builder_page_visibility_rules.htm&type=5

The mass transfer tool allows you to transfer up to 250 records at a time from one user to another user while keeping the existing team members intact. You can access this tool from Setup by entering Mass Transfer Records in the Quick Find box. References: https://help.salesforce.com/s/articleView?id=sf.
mass_transfer_overview.htm&type=5

To create a many-to-many relationship between two existing custom objects, the administrator needs to create a junction object that has two master-detail relationships, one to each of the custom objects. This will allow each record of one object to be linked to multiple records from another object and vice versa. References:
https://help.salesforce.com/s/articleView?id=sf.relationships_manytomany.htm&type=5

The Opportunity Stage Duration report is a standard report that shows how long opportunities spend in each stage before they are closed. It can be used to measure the average stage duration for all closed opportunities by grouping and summarizing the data by stage name and duration fields. Using process builder to capture the daily average on each opportunity is not feasible because it would require creating multiple fields and formulas on the opportunity object and updating them every day. Adding formula fields to track stages on each opportunity is also not practical because it would require creating multiple fields and formulas on the opportunity object and maintaining them every time a stage changes. Refreshing weekly reporting snapshots for closed opportunities is not necessary because the report can run on real-time data without snapshots.
References: https://help.salesforce.com/s/articleView?id=sf.reports_opportunity_stage_duration_report.
htm&type=5