A wood post of rectangular cross section (see figure) is constructed of structural grade, southern pine lumber

Question:

A wood post of rectangular cross section (see figure) is constructed of structural grade, southern pine lumber (Fc = 14 MPa, E = 12 GPa). The cross-sectional dimensions of the post (actural dimensions) are b = 100 mm and h = 150 mm.
Determine the allowable axial load Pallow for each of the following lengths: L = 1.5 m, 2.0 m, and 2.5 m.