Find the area of a triangle two sides of which are $18 \mathrm{cm}$ and $10 \mathrm{cm}$ and the perimeter is $42 \mathrm{cm}$.

The area of the triangle is $k\sqrt{11} {\text{cm}}^2$ . Write the value of k.

The perimeter of a triangle is $300 \mathrm{m}$. If its sides are in the ratio $3:5:7$. Find the area of the triangle.

The area of the triangle is $1500\sqrt{k } {\text{m}}^2$ . Find the value if k.

The area of the shaded region in Figure$=$_____${\mathrm{cm}}^2$.