A simple linear regression analysis is performed to determine how the strength of a substance depends on its density. Fight samples of the substance are prepared, with densities 11.2. 12.5. 13.4, 14.9, 16.0, 16.6. 17.9, and 20.1, and their strengths are found. The estimates β^0 = 75.32, β^1 = 0.0674, and σ^= 0.0543 are obtained. Calculate a 95% confidence interval for the average strength of substances with a density 15.