Answer:
Johnny is wrong.
[tex]A \cup B = \left\{a,b,c,d,e,f,g,h\right\}[/tex]
Step-by-step explanation:
Johnny is wrong.
A better definition would be: [tex]A \cup B[/tex] is the set of all elements that belong to at least one A or B.
So, the elements that belong to both A and B, like c and d in this exercise, also belong to [tex]A \cup B[/tex].
So:
[tex]A \cup B=\left\{a,b,c,d,e,f,g,h\right\}[/tex]