Hello anon user!
To make a rectangle, there would need to be 2 pairs of the same coordinate on the x-axis and 2 pairs of the same coordinate on the y-axis. (if that makes sense)
The coordinates for the x-axis:7,-4 There need to be two of each of these
The coordinates for the y-axis:2,4 There need to be two of each of these
From the first three points, there were two 7's (for the x-axis) and two 2's (for the y-axis)
To make a coordinate, you go from the x-axis location to y-axis location
Missing x-axis location:-4
Missing y-axis location:4
So the missing coordinate would be (-4,4), to make a rectangle of (7,2), (7,4), (-4,2) and (-4,4)
I hope I helped you anon!