[填空题]
In a certain library the firs;wqek 1p,ve,y t shelf is 10.0 cm off thery84kvd+ qbp 0 ground, 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 is required to fill all the shelves, assuming the books are all laying flat on t r4k+qv0d 8ybphe floor to start? $\approx$ J
