A rectangular timber beam is designed to bear a uniformly distributed load of $20$

kN over a $3\mathrm{.}6$ m span while being simply supported. The beam's depth is intended to

be twice its breadth, and the stress within the timber should not surpass $7$ MPa.

Determine the dimensions of the cross$-$section that meet these criteria.

Additionally, if the beam is subjected to a central point load of $20$ kN while

maintaining the same breadth$-$to$-$depth ratio, describe how the cross$-$section should

be modified