The following problem I just can't seem to solve:

From a set of 6 hardcover and 2 paperback books, how many different 4-book sets can be formed if each 4-book set must contain at least one paperback?

The answer says 65 ... but I have no idea how they're getting to this answer. I tried multiplying (6 3)*(2 1) (6 choose 3, 2 choose 1)... but that can't be right because the 4 book set must contain AT LEAST one paperback, so it can also contain 2.

Any help here would be much appreciated. Thanks.