An 'open pit' (khula gaddha) is by definition an empty excavated hole from which soil/material has been removed — it is not a container that has been filled with soil. The question tests careful reading: despite giving dimensions as if computing a volume, an open, unfilled pit contains zero volume of soil.
The dimensions 2 m x 2 m x 10 cm describe the size of the pit (the excavated cavity), not the amount of soil placed...
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