What is the scale factor for the dilation for the following coordinates?

N: 3.00, 1.00
O: 7.00, 2.00
P: 9.00, 5.00
Q: 4.00, 7.00
R: 3.00, 4.00

N': -6.33, 1.00
O': -7.67, 0.67
P': -8.33, -0.33
Q': -6.67, -1.00
R': -6.33, 0.00