Current Attempt in Progress

At time $t,$vec$(r)=7\mathrm{.}00t^2$hat$(i)-(6\mathrm{.}30t+4\mathrm{.}40t^2)hat(j)$ gives the position of a $3\mathrm{.}0$ kg particle relative to the origin of an $xy$ coordinate system $($ vec$(r)$ is in meters and $t$ is in seconds$).($a$)$ Find the torque acting on the particle relative to the origin at the moment $1\mathrm{.}69s(b)$ Is the magnitude of the particle's angular momentum relative to the origin increasing, decreasing, or unchanging?

$($a$)$ i $$ widehat$(k)$ Units $$

$($b$)$