A ∪ B, meaning "A union B", is the set of all elements in either A or B.

So here we have A ∪ B = {m, n, p, q, o} since all of those items are in either A or B.

(This is in roster notation already, which is simply the {} brackets surrounding an explicit list of every element in the set, as opposed to writing the set in range notation, for example [m,q].)