Answer
4,504,501 ways to store 3000 copies in three warehouses.
Work Step by Step
Ways to fill r indistinguishable books into n warehouses is given by C(n+r-1,r) .
In our case r= 3000 , n= 3
So C(3000+3-1,3000) = C(3002,3000) = 4,504,501 ways to store 3000 copies in three warehouses.