A couple usually means 2, but 'couple' and 'few' are frequently used when the actual number is unknown. Normally they mean 2 or 3, maybe 4.

A few days = usually 3+ Some people don't say exactly what they mean, and 'a few' is a vague term. It generally means 3 or more, but it's vague enough to be used sometimes when meaning 2 (slightly over-stated), or even 1 (extremely under-overstated), or even 0 (blatant lie). It generally doesn't mean a high number unless under-stating, for example when being humble. Few days (without 'a') = not many days Again this is vague. It can comfortably refer to any number, even 0, but generally doesn't refer to a high number, like thousands, which would be "a lot of days" and even "a few years". A couple (of) days = 2 days, although using the number 2 is more precise, while saying "a couple" is a bit more lenient, and is often used as an approximation, so some people will say "a couple" while meaning "about 2 or 3" for example. But the textbook answer will be a couple = 2.