Shaggy has to learn 71 hiragana characters, and has one week
to do so; he can learn as many per day as he wants. However,
Shaggy has decided to obey the advice of a study-skills professional, who has
advised him that the number of characters he learns on anyone day should
be within 4 of the number he learns on any other day.

a. What is the least number of hiragana that Shaggy could have to learn
on Saturday?
b. What is the greatest number of hiragana that Shaggy could have to
learn on Saturday?

Unable to understabd the statement in bold?