Answer
$R^2_{adj}=0.517$
It is recommended to add the new explanatory variable because it will increase the proportion of the variation of the response variable explained by the multiple regression model.
Work Step by Step
$R^2_{adj}=1-(\frac{n-1}{n-k-1})(1-R^2)=1-(\frac{40-1}{40-5-1})(1-0.579)=0.517$
