Reflecting over the y axis simply means that all the coordinates of y will remain constant while that of x becomes - x. See it below:
A (-4, 5) = A' (4, 5)
B (-2, 4) = B' (2, 4)
C (-2, 1) = C' (2, 1)
D (-4, 1) = D' (4, 1)
We therefore see that based on the x coordinates, the trapezoid lies in the Second quadrant