The cost of cultivating a rectangular field at $₹35$per square metre is $₹71400.$ If the width of the field is $40 \mathrm{m},$ find its length. Also, find the cost of fencing the field at $₹50$ per metre.

If the area is k ${\text{cm}}^2$ , then write the value of k.

Calculate the area of the shaded region given below:

If the area is k ${\text{m}}^2$ , then write the value of k.

The area of the shaded region given below$=$_____${\mathrm{m}}^2$.

The area of the shaded region given below$=$_____${\mathrm{m}}^2$.

The area of the shaded region given below$=$_____${\mathrm{cm}}^2$. (all measures are given in $\mathrm{cm}$):