The relevant information is: A week is a time unit equal to seven days.
This justifies what answer for what question? Q & A: 
Passage: A week is a time unit equal to seven days. It is the standard time period used for cycles of rest days in most parts of the world, mostly alongside -- although not strictly part of -- the Gregorian calendar.

Question: Based on this passage, 1 week is equal to how many days?
seven