What is the difference between "in" and "within"?

Solution 1:

Within is closer to inside - it mainly refers to something like a building where you are physically in (or inside).

In can also mean a state or an organisation, so you can be "in trouble", or "in school" but not "within trouble".

In- A limit of some sort.

i.e. "In 6 days,..."

You limit the time in the sentence exactly.

Within- Inside the said limit.

i.e. "Within 6 days,..."

You limit the time in the sentence, but inside the said time.