A bicycle tire is spinning counterclockwise at 3.40 rad/s. During a time period t = 1.50 s, the tire is stopped and spun in the opposite (clockwise) direction, also at 3.40 rad/s. Calculate the change in the tire's angular velocity and the tire's average angular acceleration _av. (Indicate the direction with the signs of your answers.)

(a)the change in the tire's angular velocity (in rad/s)

(b)the tire's average angular acceleration _av (in rad/s²)