The smallest size of a hybrid bike, a bike that can be ridden both on and off dirt, is 16.9 inches . Bikes are fitted using a person's inseam with the smallest inseam for a hybrid bike being 25 in. For inseams 25 inches ( in .) or longer, each 0.68 of an inch increase in bike size, a person's inseam is 1 inch longer. A medium size bike has a range of 20.9 in. to 22 in. Write an inequality, where x is the length of an inseam, in inches, that can be used to determine the inseam sizes that best fit a medium size bike.​