Given
The perimeter of square plot $$=360\ m$$
Hence,
Side of square plot = Perimeter $$/4$$
$$=360\ m/4$$
We get,
$$=90\ m$$
Therefore the side of square plot $$=90\ m$$
Given
The cost of leveling $$=Rs. 60$$ per square meter
Cost of leveling can be calculated as follows:
Cost = Area $$\rimes $$ Rate
$$=8100\ m^2 \times 60$$
We get,
$$=Rs. 486000$$
Therefore, the cost of leveling the plot $$=Rs. 486000$$