At time t$,$ r$=1\mathrm{.}10$t$^2-(3\mathrm{.}00$t $+3\mathrm{.}40$t$^2)$ gives the position of a $3\mathrm{.}0$ kg particle relative to the origin of an xy coordinate system $($is in meters and t is in seconds$).($a$)$ Find the torque acting on the particle relative to the origin at the moment $2\mathrm{.}78$ s $($b$)$ Is the magnitude of the particle's angular momentum relative to the origin increasing, decreasing, or unchanging?