To fint the length first one must find circumference to do that we use the formula D*Pi (diameter times Pi. Diameter = 8 Pi is the constant of 3.1415 so. 8*3.1415 = appox 25.1327. cow that we have circumference we should multiply by the amount of times the wheel rotates (15) so. 15*251327 = appox 376.9911in now convert to feet. 12 in = 1 foot so divide by 12 so 376.9911 / 12 = about 31.4 round down to 31 feet