The growth of cell culture (optical density) at various pH levels are tabulated in the following table.

pH (x)	3.5	4	4.5	5	5.5	6	6.5	7	7.5
Optical density (y)	0.2	0.25	0.34	0.42	0.48	0.53	0.56	0.61	0.64

Calculate coefficients a and b in

y = ax²/(b+ x²)

to be a least squares fit to the data in the table.