A homogeneous gravity retaining wall supporting a cohesionless backfill is shown in the figure. The lateral active earth pressure at the bottom of the wall is $40$ kPa.

The minimum weight of the wall (expressed in kN per m length) required to prevent it from overturning about its toe (Point $\color{Red}{P}$) is

1. $120$
2. $180$
3. $240$
4. $360$