The window of the house is in the form of a rectangle surmounted by a semi-circular position having a perimeter of 10 m as shown in figure. If x and y represent the length and breadth of rectangular region the whole area of whole window is maximum, then value of x is :

$\frac{20}{\pi }$ $\frac{20}{4-\pi }$ $\frac{20}{2+\pi }$ $\frac{20}{4+\pi }$

$\frac{20}{4+\pi }$