30 minutes later, they would be located at (4,- 4)
To see this......note that they would have rotated (2 x 90) degrees = 180 degrees in 30 minutes
And (-4, 4) is located on the line y = -x
And since a line is a straight angle measuring 180 degrees, then (4, -4) is also on this line, rotated 180 degrees from (-4, 4)