At timet, $7=7\mathrm{.}40$t$2-(9\mathrm{.}00$t $+4\mathrm{.}20$t$2)$ j gives the position of a $3\mathrm{.}0$ kg particle relative to the origin of

an xy coordinate system $($ r is in meters and t is in seconds$).($a$)$ Find the torque acting on the particle

relative to the origin at the moment $4\mathrm{.}96$ s $($b$)$ Is the magnitude of the particle's angular momentum

relative to the origin increasing, decreasing, or unchanging?