Your height: 5'3" to 5'8" (160 to 172cm) approximatly (?).
Frame size = 20in/51cm
Comments:
Mountain Bikes: they are sturdy and designed to go everywhere including off-road. Good for rough riding. In general heavy and with deep thread tires slow on paved roads. Not good city bikes unless narrower and slick tires are installed.
21 speed: perfect to go everywhere including going up very steep hills. There are 3 front chain rings and 7 rear gears. - Derailleur: Shimano SIS
Tires 26 x 1.95: wide tires, deep thread, all terrain.