If you were to rotate ABCD 180° about the origin, what would the coordinates of B' be?
(-1,3)
(0,0)
(-6, -5)
(-6, 2)

both elements will be negative in rot.180°

for finding the midpoint of any given 2 pair of points simply add the respective x coordinates with other x coordinate and the y coordinate with other y coordinate and divide them by 2

in your question it will be :

(3+1)/2 for the x coordinate of mid point i.e 2

[8+(-4)]/2 for the y coordinate of midpoint i.e 2

so coordinates of mid point of points (3,8) and (1,-4) will be (2,2)