John's parents recorded his height at various ages up to 66 months. Below is a record of the results.

Age (months) 36 48 54 60 66
Height (inches) 35 38 41 43 45

We conclude John's height, in inches, should be about half his age, in months. the parents will get a fairly accurate estimate of his height at age 21 years because the data are clearly correlated, such a prediction could be misleading because it involves extrapolation.

a. Determine the equation of the least-squares regression line of John’s height on age.
b. John’s parents decide to use the least-squares regression line of John’s height on age to predict his height at age 21 years (252 months). What conclusion can we draw?