You must consider the three couples of points, before and after the dilation.
The bottom-left point was (3,3) and it becomes (4,5). The line connecting these two points is y = 2 x - 3
The bottom-right point was (6,3) and it becomes (10,5). The line connecting these two points is y = x/2
The top point points was (5,4) and it becomes (8,7). The line connecting these two points is y = x-1.
Those three lines meet at (2,1), and thus this is the center of dilation.
