The stresses developed in concrete and steel in reinforced concrete beam 25 cm width and 70 cm effective depth are 62.5 $$\frac{kg}{cm^{2}}$$ and 250 $$\frac{kg}{cm^{2}}$$ respectively. If m= 15, the depth of its neutral axis is

A

20 cm

B

25 cm

C

30 cm

D

35 cm