Increases in the mortgage interest rate increase the cost of owning a house and lower the demand for houses. In this question, we use three equations to forecast the monthly change in the number of new one-family houses sold in the United States. In the first equation (XR 9.12.1), the monthly change in the number of houses DHOMES is regressed against two lags of the monthly change in the 30-year conventional mortgage rate DIRATE. In the second equation (XR 9.12.2), DHOMES is regressed against two lags of itself, and in the third equation (XR 9.12.3), two lags of both DHOMES and DIRATE are included as regressors.