Answer
B' = {a,b,f,g}
Work Step by Step
U = {a,b,c,d,e,f,g}
B = {c,d,e}
Find A'
Set B' includes all the elements in 'U' that are not in set B.
Since set B contains c,d,e so these elements cant be in set B.
Therefore the elements of set B' are a,b,f,g.
Therefore B' = {a,b,f,g}