A rigid horizontal bar ABC, with roller support at A, is pinned to the columns BD and CE at points B and C, respectively, as shown in the figure. The other end of the column BD is fixed at D, whereas the column CE is pinned at E. A vertical load P is applied on the bar at a distance 'a' from point B.
The two columns are made of steel with an elastic modulus of 200 GPa and have a cross-section of 1.5 cm x 1.5 cm. The value of 'a' for which both columns buckle simultaneously, is _______ cm. (round off to one decimal place).