It seems there is no dealership in patna, you can contact your nearest city dealership to get the car. You can follow the site for know about thenearest dealers to your city: http://www.cardekho.com/Renault/cardealers
PS is the German unit of power, 85 PS means that this car generates 85 PS of power and RXE is the name of the variant. It has got a 110 PS variant also which means that the engine is tuned to generate 110 PS of power.
The petrol variants of Duster and Terrano return a low mileage of around 12-13 kmpl, therefore it is advisable to go with diesel variants. Also, the K9K diesel engine performs better than the 1.6-litre petrol engine.