A wood column of rectangular cross section (see figure) is constructed of structural grade, Douglas fir lumber

Question:

A wood column of rectangular cross section (see figure) is constructed of structural grade, Douglas fir lumber (Fc = 12 MPa, E = 10 GPa). The cross-sectional dimensions of the column (actual dimensions) are b = 140 mm and h = 210 mm.
Determine the allowable axial load Pallow for each of the following lengths: L = 2.5 m, 3.5 m, and 4.5 m.