In 1 full revolution, the bike will travel 42 inches because the diameter of the tire is 21 inches. Any point on the tire will have to go through a whole revolution to be back at the original point which means 21 inches times 2.
So the bike travels 42 inches in 1 revolution then in 50 revolutions it will travel 2100 inches (42 times 50). Now if your convert 2100 inches to feet, you get 175 feet.
