A regression of y = calcium content (g/L) on x = dissolved material (mg/cm²) was reported in the article “Use of Fly Ash or Silica Fume to Increase the Resistance of Concrete to Feed Acids” (Mag. Concrete Res. 1997: 337–344). The equation of the estimated regression line was y = 3.678 + .144x, with R² = .860, based on n = 23.

a. Interpret the estimated slope .144 and the coefficient of determination .860.
b. Calculate a point estimate of the true average calcium content when the amount of dissolved material is 50 mg/cm².
c. The value of total sum of squares was SST = 320.398. Calculate an estimate of the error standard deviation σ in the simple linear regression model.