71. It is not safe to drive a vehicle that has brake drums with cracks that are longer than ____ of the width of the friction area.
1/2
72. To test air service brakes you should:
Brake firmly while slowly moving forward.
73. If you are driving down to the steep downgrade and you have reached the speed of 40 mph, you would apply the service brake until your speed dropped to below ____ mph.
35