Solution to Example 6.11, Problem 2
The x values in the data are between 65 and 75. 90 is outside of the domain of the observed x values in the data (independent variable), so you cannot reliably predict the final exam score for this student. (Even though it is possible to enter x into the equation and calculate a y value, you should not do so!)
To really understand how unreliable the prediction can be outside of the observed x values in the data, make the substitution x = 90 into the equation.
The final exam score is predicted to be 261.19. The largest the final exam score can be is 200.