Final answer:
To correctly format the string to right-align 'Day' with underscores padding to a length of 10 characters, the format string should be '{:>10}'.format('Day').
Step-by-step explanation:
The student is asking how to complete a Python format string to produce a specific output. Given the format string provided, >>>{v8:'_'}_format('Day'), it seems that there's a syntax error, and what the student likely needs is a correct format() method call to format a string with an underscore ('_') padding.
To achieve the desired output that displays the word 'Day' right-aligned with underscores padding to the left, the correct format string should look like this:
>>> '{:>10}'.format('Day')
This format string will align 'Day' to the right, padding with underscores until the total string length is 10 characters.