If B={3,6,9,12,15,18,21} C={3,6,9,12,15,18,21} and D={6,12,18,24} . What is B-C-D

I take B - C - D to mean (B - C ) - D, i.e. all elements of B - C not in D, or all elements in B not in C and not in D.

The given sets B and C are identical, so

B = {3, 6, 9, 12, 15, 18, 21}

C = {3, 6, 9, 12, 15, 18, 21}

===>   B - C = { }

Then

(B - C ) - D = { } - D = { } (empty set)

i think this could be a possible answer (1 / 84) -1

good luck! : d