Jeep TJ Classic Men's 21 speed mountain bike

This Jeep Mountain Bike has 21 gears that can be adjusted by rotating the handlebars. The height to the handlebars is around 42 inches and wheel size is around 26" in diameter. Note that the innertube on the rear tire is currently flat. I don't know how to personally change an innertube and I don't want the expense of getting it changed at a repair shop before selling the bike. So please only purchase this bike if you either know how to change the inner tube or if you plan to take it to a shop to get it replaced.