Confidence intervals for the average response at specific values

The previous two exercises gave CIs for the slope parameter. That is, based on the observed data, you provided an interval estimate of the plausible values for the true slope parameter in the population. Recall that the number 1 was in the CI for the slope, meaning 1 cannot be ruled out as a possible value for the true slope between Biological and Foster twins. There is no evidence to claim that there is a difference, on average, between the IQ scores of two twins in any given pair.

When working with a linear regression model, you might also want to know the plausible values for the expected value of the response at a particular explanatory location. That is, what would you expect the IQ of a Foster twin to be given a Biological twin's IQ of 100?