Answer
B$^\prime$={1,2,3,5,7,15}
Work Step by Step
B$^\prime$ includes all the members of U that are not members of B. List the members of U, and cross out the ones that are members of B. The remaining are members of B$^\prime$.
$\{1, 2, 3, /\!\!\!4, 5, 7, /\!\!\!8, /\!\!\!\!12, 15\}$
