A rectangular solid timber beam $100 mm$ wide ($b$) and $200 mm$ deep ($h$) is subjected to a maximum internal bending moment of $15 kN\cdot\text{m}$. Determine the absolute maximum flexural stress developed in the timber.

A rectangular timber beam $150 mm$ wide and $250 mm$ deep is subjected to a maximum vertical shear force of $40 kN$. Determine the maximum horizontal shear stress in the beam.