In a bord and pillar panel, a square pillar of size 35 m×35 m (centre to centre) is extracted to form four equal square-shaped stooks as shown. The width of each gallery and crosscut is 5 m. The height of the working seam is 3 m. The reduction in safety factor after pillar splitting by using Bieniawski's pillar strength formula, in %, is ______ (rounded off to 2 decimal places)
Bieniawski's pillar strength formula, S_p=S₁(0.64+0.36(w/h)); where, S₁= strength of 0.9 m³ of coal block, w= pillar width and h= mining height