what are the gas mileage and what about the whole car
Gas mileage , who knows . It all depends on your driving pattern , all city or all highway. A simple web search will find that for you and as for the vehicle that needs to be determined by a mechanic before you buy if that is the reason for this vague question.
Pretty sure the Trax was first introduced as a 2015 model year car in the U.S. Here is the fuel economy for that model: https://www.fueleconomy.gov/feg/PowerSearch.do?action=noform&path=1&year1=2015&year2=2015&make=Chevrolet&baseModel=Trax&srchtyp=ymm
Are you in the USA? The first model year available in the US is 2015. Since most of the posters here live in North America, we wouldn’t know much about the 2014.
2014 Trax was sold in Canada apparently. I’m seeing some problems reported w/the steering, tracking & fluid leaks. Recalls for updating body control module, rear seat belt problem, mechanical interference involving front brakes, fuel system connectors not fully secured, windshield wiper motor problem, ignition key cylinder wear causing self-cranking, other minor items. Nothing too serious, but suggest to obtain the full recall list and makes sure those have all been taken care of.