In a circle, the length of an arc of central angle $25°$ is 4 centimetres. In a circle of radius one and a half times the radius of this circle, what is the length of an arc of central angle $75°?$ Write the answer in centimetres.

The picture shows the parts of a circle centered at each vertex of an equilateral triangle and passing through the other two vertices. What is the perimeter of this figure? Write the answer in centimetres.

Parts of circles are drawn, centered at each vertex of a regular octagon and a figure is cut out as shown below:

Calculate the perimeter of the figure. Write the answer without unit and up to $2$ decimal places. Take $\mathrm{\pi }=3.14$

Calculate the area of the green-colored part of this picture. 

Centered at each corner of a regular hexagon, a part of a circle is drawn and a figure is cut out as shown below:

What is the area of this figure? Write the answer without unit and up to $3$ decimal places. Take $\mathrm{\pi }=3.14, \sqrt{3}=1.732$.

The picture below shows two circles, each passing through the center of the other:

Calculate the area of the region common to both. Write the answer in ${\mathrm{cm}}^2$.