We can find this thusly
Post Image Vertex = [Pre-Image Vertex - DilationCenter]*Scale Factor + Dilation Center
So we have
(7,2) = [ (-5, -2) - (-2, -2) ] * Scale Factor + (-2, -2)
(7,2) = [ (-3, 0 )] * Scale Factor + (-2,-2)
(7,2) - ( -2, -2) = (-3, 0) * Scale Factor
( 9, 0) = (-3, 0) * Scale Factor
9 / -3 = Scale Factor
-3 = Scale Factor
