[填空题]
In a certain library the first shelf is 10:n:)/ jnc * s-vbchxsy.0 cm off the grnd,7i0j*1sk mk(k lxp 5g/wfv ound, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work ismn, vkkf1 ikws (dpx5/g0j*7l required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$ J
