You have six cards, and there is a number on the face of each card, from 1 through 6.

You are going to rearrange these 6 cards in one row. (a) What is the probability that the cards with 1, 2, and 3 are adjacent to each other? (e.g. 123456 or 413256.)

(b) What is the probability that the cards with 3 and 4 are located in the both ends of the row? (e.g. 312564 or 412563.) Note that, in this problem, 1, 2, and 3 do not need to be adjacent.