A particle of mass 'm' is moving in time 't' on a trajectory given by

$\overrightarrow r = 10\alpha {t^2}\widehat i + 5\beta (t - 5)\widehat j$

Where $\alpha$ and $\beta$ are dimensional constants.

The angular momentum of the particle becomes the same as it was for t = 0 at time t = ____________ seconds.