b$)$ A study was performed on a type of bearing to find the relationship of amount of wear $y$ to

$x_1=$ oil viscosity and $x_2=$ load. The following data were obtained.

i$)$ Compute ${\displaystyle \underset{?}{\overset{?}{}}}y,{\displaystyle \underset{?}{\overset{?}{}}}{x}_1,{\displaystyle \underset{?}{\overset{?}{}}}{x}_2,{\displaystyle \underset{?}{\overset{?}{}}}{x}_1{x}_2,{\displaystyle \underset{?}{\overset{?}{}}}{x}_{1}y,{\displaystyle \underset{?}{\overset{?}{}}}{x}_{2}y,{\displaystyle \underset{?}{\overset{?}{}}}{x}_1^2$ and ${\displaystyle \underset{?}{\overset{?}{}}}{x}_2^2$

ii$)$ Estimate the unknown parameters of the multiple linear regression equation using

Normal equations. ${}_{Y|x_1,x_2}={}_0+{}_1{x}_1+{}_2{x}_2.$

iii$)$ Predict wear when oil viscosity is $20$ and load is $1200.$

iv$)$ Find the multiple co$-$efficient of correlation $R$ and co$-$efficient of determination $R^2$