Quantity A
1/2y-1/2x

Quantity B
0

where

X<Y<-1


When I attempt to answer the question my self , I was thinking in different way
I just substitute the variables x and y with the suitable values based on the information given that x<y<-1
So I set x to be -3 and y to be -2 and they all less than -1 as above.
Then I plug in that values in the equation 1/2y-1/2x
I get 1/2(-2)-1/2(-3)
then I continue 1/-4-1/-6
and because I have 1/-4 , then I can rewrite it -1/4 , the same for the other fraction 1/-6 I rewrite it to be -1/6
then -1/4-(-1/6) means -1/4+1/6 because we have two negative signs
then I put a common denominator 2
and then I get -2+3/2 which equal to 1/2 which is greater then Quantity B (0) so my answer was A for that question but I discovered from the video that my answer is wrong and the right answer for that question is B.
I still do not know what was wrong with my solution above ?? why it is wrong ? is it the logic wrong or the approach itself wrong ?

I am sorry that my explanation took that long
I will really appreciate your help