The sides of a triangular field  are 120 m, 170 m and 250 m.The cost of levelling the field at the rate of ₹7.40/m$$^2$$ is:

sides of field a=120m,b=170m,c=250m.

semiperimeter of field s=$$\dfrac{a+b+c}{2}$$

$$\rightarrow s=\dfrac{120+170+250}{2}$$m

$$\rightarrow s=\dfrac{540}{2}$$m

$$\rightarrow s=270m$$

area of field by heron's formula,

$$\rightarrow$$ area A=$$\sqrt{s(s-a)(s-b)(s-c)}unit^2$$

$$\rightarrow$$ A=$$\sqrt{270(270-120)(270-170)(270-250)}m^2$$

$$\rightarrow$$ A=$$\sqrt{270\times150\times100\times20}m^2$$

$$\rightarrow$$ A=$$9000m^2$$

$$\rightarrow$$ total cost =$${9000\times7.40}$$rs

$$\rightarrow=66600rs$$