We can determine this as follows
New Point = (Old corresponding point - Dilation Center) * Scale Factor + Dilation Center
(5, -2) = [ ( -5, -2) - (-3, -2) ] *Scale Factor + (-3, -2)
( 5, - 2) - ( -3, - 2) = [ (-2, 0) ] *Scale Factor
( 8 , 0 ) = ( - 2, 0) * Scale Factor
(8, 0) = (-2, 0) * ( -4)
So....the scale factor is -4