The linear regression results below are based on commercial properties that real estate agencies use to guide clients with quantitative information helpful to make rental decisions. A random sample of 28 properties are considered with data for the variables, age of the property (X1), operating expenses and taxes (X2), vacancy rates (X3), total square footage (X4), and rental rates (Y).

What is the upper limit of the 95% confidence interval estimate for the effect of a square footage increase on the mean rental rates of properties?