Question

Given A = {a, e, i, o, u} and B = {a, l, g, e, b, r}, find A ∪ B.

Answer 1

$A \cup B$ indicates you want the UNION of sets A and B.  So just make a list of elements that are in either set ("put all the elements into one 'box'").  Elements are listed only once; example:  a is in both sets, so put it in the union only once.

Answer: the 3rd choice, {a, b, e, g, i, l, o, r, u}

Answer 2

A={a,e,i,o,u}   B={a,l,g,e,b.r}

A ∪ B = {a,e,i,o,u,l,g,b,r}

For any element ∈ A and B, you choose it once