The top width and the bottom width at river thalweg level of concrete gravity dam are 6 m and 24 m respectively. The vertical section of the dam at the thalweg alignment is 38 m above the thalweg. The upstream face is vertical and the depth of water on the upstream side is 36 m. The moment of hydrostatic force about the toe at that level is

• A. 77760 kN-m
• B. 25292 kN-m
• C. 6480 kN-m
• D. 51840 kN-m