Answer
{June,Jill,Jeffrey,Janet,Jello,Justin,Sally,Solly,Molly,Jolly}
Work Step by Step
$A \cup B$ is the set of all things that are members of either A or B
$A\cup B$={Janet,Jello,Justin,June,Jill,Jeffrey}
$(A\cup B)\cup C$={June,Jill,Jeffrey,Janet,Jello,Justin,Sally,Solly,Molly,Jolly}