A shallow strip footing of width 2 m is embedded at a depth of 1.5 m below the ground surface in a homogeneous pure clay with angle of internal friction equal to zero. The unit weight of soil is 20 kN/m3 and the undrained cohesion of soil is 20 kN/m2. Due to a rise of the ground water table from far below the founding depth to the ground surface during the monsoon season, the magnitude of percentage change in the net ultimate bearing capacity of the footing as per Terzaghi's theory is ______ (rounded off to two decimal places).