Which of the following represents the best way to calculate area of shaded region?

The correct answer for the exercirse shown in the figure attached is the first option, which is: Calculate the area of the circle A and circle B and calculate the difference.

 To calculate the area of the circle A and the circle B, you must apply the formula for calculate the area of a circle, which is shown below:

 A=πr²

 A is the area of the circle.
 r is the radius of the circle.

 To calculate the difference, you only have to substract the result of the area of the circle A and the area od the circle B:

 At=Aa-Ab