A combined trapezoidal footing of length \( L \) supports two identical square columns \( P_1 \) and \( P_2 \) of size \( 0.5 \, \text{m} \times 0.5 \, \text{m} \), as shown in the figure. The columns \( P_1 \) and \( P_2 \) carry loads of 2000 kN and 1500 kN, respectively.
If the stress beneath the footing is uniform, the length of the combined footing L (in m, round off to two decimal places) is \(\underline{\hspace{1cm}}\).