To create the Position column, you should use the FIRST () function. The FIRST () function returns the number of rows from the current row to the first row in the partition. For example, the first row in a partition will return 0, the second row will return -1, and so on. In this question, the partition is defined by the Segment field, and the table is sorted by the Sales field in descending order. Therefore, the Position column shows the offset of each row from the first row in each segment, based on the sales ranking. References:
Tableau Certified Data Analyst Exam Prep Guide, page 11, section "Creating Calculated Fields" Tableau Help: FIRST Function

Common Characters: Find and group values that have letters or numbers in common. This option uses the ngram fingerprint algorithm that indexes words by their unique characters after removing punctuation, duplicates, and whitespace. This algorithm works for any supported language. This option isn't available for data roles. For example, this algorithm would match names that are represented as "John Smith" and "Smith, John" because they both generate the key "hijmnost". Since this algorithm doesn't consider pronunciation, the value "Tom Jhinois" would have the same key "hijmnost" and would also be included in the group.

The correct Level of Detail (LOD) expression to calculate the grand total of sales across all regions would be
{SUM(Sales)}. The FIXED expression is not needed here because we are not computing the sum at the level of each region, but rather the total sum across all regions. The FIXED keyword is typically used to aggregate at a certain level regardless of the view.
https://help.tableau.com/current/pro/desktop/en-us/functions_functions_tablecalculation.htm#TOTAL

check the steps below in explanation.
Explanation:
To split the Customer Name field into two fields named First Name and Last Name, you need to do the following steps:
* Open the link to Book1 found on the desktop. This will open the Tableau workbook that uses the Superstore data source.
* Go to the Data Source tab at the bottom of the workbook to see the data source page. You will see a table that shows the fields and values from the Superstore data source.
* Right-click on Customer Name in the table and select Split from the menu. This will split the field into two fields based on a separator, which is a space by default. You will see two new fields named Customer Name - Split 1 and Customer Name - Split 2 in the table.
* Right-click on Customer Name - Split 1 and select Rename from the menu. Type First Name as the new name and press Enter. This will rename the field as First Name.
* Right-click on Customer Name - Split 2 and select Rename from the menu. Type Last Name as the new name and press Enter. This will rename the field as Last Name.
References: https://help.tableau.com/current/pro/desktop/en-us/datasource_prepare.htm https://help.tableau.com/current/pro/desktop/en-us/split.htm https://help.tableau.com/current/pro/desktop/en-us/renamefield.htm