According to the official documentation, the following are the requirements for using relationships:
1) When relating tables, the fields that define the relationships must have the same data type. Changing the data type in the Data Source page does not change this requirement. Tableau will still use the data type in the underlying database for queries.
2) You can't define relationships based on geographic fields.
3) Circular relationships aren't supported in the data model.
4) You can't edit relationships in a published data source.
5) You can't define relationships between published data sources.
6) Your workbook must use an embedded data source for you to be able to edit relationships and performance options in the Data Source page in Tableau Online or Tableau Server.

The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns. Consider 2 tables "Orders" and "Customers".
If there are records in the "Orders" table that do not have matches in "Customers", these orders will not be shown!

You can export the data in a Tableau data source, including all or part of the records from your original data. Alternatively, you can export only the portion of data used to generate the view.
Since the question mentions the data used to build the view, we'll focus on that :
*Export data in the view to Microsoft Access or .csv*
Export the data that is used to generate the view as an Access database (Windows only) or .csv file (Mac only).
1) In Tableau Desktop, select Worksheet > Export > Data.
2) Select a location and type a name for your Access database or .csv file.
3) Click Save.
4) If you're on Windows, the Export Data to Access dialog box displays to give you the option to immediately use the new Access database and continue working in Access without interrupting your work flow.

Line charts connect individual data points in a view. They provide a simple way to visualize a sequence of values and are useful when you want to see trends over time, or to forecast future values.
Please refer to the images below:

Explanation
We need to use the concept of Groups for this question. Follow along:
1) First, Drag State to the Rows shelf, and Total Expenses to the Text Mark on the Marks Shelf:

2) Now, remove the SUM aggregation from Total Expenses, and add a quick table calculation -> Percent of total:

3) Next, Select the States of New York, California and Washington -> And then click the paperclip icon:

We can see the answer already : 23.386% in the view above (even before grouping!)
4) Finally, we get the following view and our answer: