A bicycle tire is spinning clockwise at $2\mathrm{.}50$ rad$/$s$.$ During a timeperiod At $=1\mathrm{.}25$ s$,$ the tire is stopped and spun in the opposite $($counterclockwise$)$ direction, also at $2\mathrm{.}50$ rad$/$s$.$ Calculate$($a$)$ the change in the tire's angular velocity Aw and $($b$)$ the tire's average angular acceleration dav.