To the nearest inch, the diameter of the tire is 26 inches.
The bike traveled 136 feet in 20 revolutions. First we want to convert this to inches.
136 ft * 12 in/ft = 1632 inches.
Next we find how many inches it travels in 1 revolution:
1632/20 = 81.6 inches
The distance around the tire is called the circumference, and the formula for circumference is
C=πd
Our circumference is 81.6 and π is 3.14:
81.6 = 3.14d
Divide both sides by 3.14:
81.6/3.14 = 3.14d/3.14
26 = d