Two medians NA and OB of $$\triangle$$NOP intersect each other at S at right angles. If NA = 15 cm and OB = 15 cm, then what is the length of OA?

A

$$5\surd{5}$$ cm

B

$$7\surd{5}$$ cm

C

$$6\surd{5}$$ cm

D

$$3\surd{5}$$ cm