At an urban pedestrian crosswalk, the inital WALK signal is displayed for 6.0 sec, after which a flashing DON'T WALK signal is displayed. The pedestrian walking speed is 3.5 ft/sec, and the street to be crossed is 31.5 ft wide. At the end of the green time, the flashing DON'T WALK signal is terminated. The minimum length of time(sec) the green must be displayed is most nearly?

a) 9.5
b) 15.0
c) 22.0
d) 22.5