The following sample data were collected to determine the relationship between two processing variables and the current gain of a transistor in an integrated circuit.

Diffusion time in hours (x1​)	Sheet resistance ohm-cm (x2​)	Current gain (y)
1.5	65	5.2
1.2	140	9.8
0.5	70	7.5
2.7	92	10.8
1.6	123	12.6
0.3	105	9.1

(i) Fit a regression equation and use this equation to estimate the expected current gain when the diffusion time is 1.8 hours and the sheet resistance is 90 ohm –cm.

(ii) Compute the coefficient of multiple determination and interpret its value.