[填空题]
In a certain library th a:qhskjkfh/nn g q8(2qx88*eeznhyif16m. x3h3gx ay.l; uo) first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the prev.g ;1o.namz)h yx 63lfiy3huxious 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 is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$ J
