python2.7 出错NameError: name 'cars_driven' is not defined

代码如下：# -- coding: utf-8 --cars = 100 space_in_a_car = 4 #4.0是float，浮点数drivers = 30passengers = 90cars_not_driven = cars - driverscar_driven = driverscarpool_capacity = cars_driven * space_in_a_caraverage_passengers_per_car = passengers / cars_drivenprint "There are",cars,"cars available."print "There are only", drivers,"drivers available."print "There will be", cars_not_driven, "empty cars today."print "There car_driven:", car_drivenprint "We can transport ", carpool_capacity, "people today."print "We have", passengers, "to carpool today."print "We need to put about ", average_passengers_per_car, "ineach car."错误信息如下：Traceback (most recent call last): File "C:\Users\Administrator\Desktop\python_work\ex4.py", line 8, in <module> carpool_capacity = cars_driven * space_in_a_carNameError: name 'cars_driven' is not defined图片：