i think answer should be A.though i am not geting the xact answer.
P(X>b|X<b/2) = P(X>b and X< b/2)/ P(X<b/2)
now,it is given that -1 < b < 0
so, -1/2 < b/2< 0
hence P(X< b/2) = integral [3x2]b/2 -1/2 = [x3] b/2-1/2 = b3 /8 + 1/8
and P(X > b and X< b/2 ) = [x3] b/2b =-7b3/8
hence,answer is -7b3/b3 + 1
so might be i am wrong somewhere and answer is A.
please confirm