The efficiency for a steel specimen immersed in a phosphating tank is the weight of the phosphate coating divided by the metal loss (both in mg/ft2). An article gave the accompanying data on tank temperature (x) and efficiency ratio (y). Temp. 171 173 174 175 175 176 177 178
Ratio 0.82 1.21 1.50 1.05 1.01 1.06 0.98 1.74

Temp. 181 181 181 181 181 182 182 183
Ratio 1.39 1.54 1.69 2.05 2.13 0.86 1.35 0.82

Temp. 183 183 183 185 185 186 187 189
Ratio 1.83 1.96 2.66 1.51 2.44 2.98 1.91 3.02

Required:
a. Determine the equation of the estimated regression line.
b. Calculate a point estimate for true average efficiency ratio when tank temperature is 182.
c. Calculate the values of the residuals from the least squares line for the four observations for which temperature is 182.