Answer
It is not recommended to add the new explanatory variable because it will reduce the proportion of the variation of the response variable explained by the multiple regression model.
Work Step by Step
$R^2_{adj}=1-(\frac{n-1}{n-k-1})(1-R^2)=1-(\frac{25-1}{25-4-1})(1-0.665)=0.598$
