The correct answer is {1, 2, 5, 6}.
A intersect B would be {3, 4}; the complement of this is everything else.
it would be a because nothing else makes sense
To simplify 7C4 we use the combination formula given by:
nCr=n!/[(n-r)!r!]
thus:
In our case we shall have:
n=7 and r=4
7C4
=7!/[(7-4)!4!]
=5040/[6×24]
=5040/144
=35
The answer is 35
