The top width and the top depth of flow in a triangular channel were measured as $4$ m and $1$ m, respectively. The measured velocities on the centre line at the water surface, $0.2$ m and $0.8$ m below the surface are $0.7$ m/s, $0.6$ m/s and $0.4$ m/s, respectively. Using two-point method of velocity measurement, the discharge (in $m^3/s$) in the channel is
- $1.4$
- $1.2$
- $1.0$
- $0.8$