A particle of mass $0.5\ \text{kg}$ moves at a steady $2\ \text{m/s}$ along the straight line $y = 3\ \text{m}$, in the $+x$ direction, as shown in the figure. The magnitude of its angular momentum about the origin, in $\text{kg m}^2/\text{s}$, is ____.

Fig. 1: x and y axes with origin O. A 0.5 kg particle moves at 2 m/s in the positive x-direction along the dashed line y = 3 m; its position vector r is drawn from O.