For the planking and strutting shown below calculate the length of timber required in meters for the poling boards, walling and struts for an excavation of 150 meters lengt h. Assume the length of each poling board to bei meter. Show all your workings 100 x 100 mm struts at 1.8 m centres 100 x 100 mm waling 175 x 38 mm poling boards 300 mm apart 100 x 100 mm waling​