A timber beam of rectangular section of length 8 m is simply supported .The beam carries a uniformly distributed load of 12 $$\frac{kN}{m}$$, over the entire length and a point load of 10KN at 3m from the left support .If the depth is two times the width and the stress in the timber is not to exceed 10 $$\frac{N}{mm^{2}}$$, what is the suitable depth of the section?

A

412 mm

B

512 mm

C

612 mm

D

712 mm