Table 5.

Estimated regression coefficients, t-values and p-values.

Term	Zn Removal
	Coefficient	T-Value	P-Value
β0	28.61	11.27	0.00
β1	−23.84	−14.16	0.00
β2	11.49	6.83	0.00
β3	−1.76	−1.04	0.32
β11	4.96	3.03	0.01
β22	2.44	1.49	0.17
β33	−1.53	−0.93	0.37
β12	−7.38	−3.35	0.01
β13	5.56	2.53	0.03
β23	5.72	2.60	0.03