In the given figure, PQRS is a rectangle and a semicircle with SR as diameter is drawn. A circle is drawn as shown in the figure. If QR = 7 cm, then what is the radius (in cm) of the small circle?

A

$$21 + 14\surd2$$

B

$$21 - 14\surd2$$

C

Both $$21 + 14\surd2$$ and $$21 - 14\surd2$$

D

None of these