That 10 is the diameter of the circle.
First let's find the area of the square.
A = s^2
Where 's' is the side.
A = 10^2
A = 100
Now let's find the area of the circle.
The '10' is also the diameter of the circle.
A = pi * r^2
A = 3.14 * 5^2
A = 3.14 * 25
A = 78.5
Now subtract this from the area of the square.
100 - 78.5 = 21.5
So the approximate area of the shaded region is 21.5cm^2