Question

In how many ways can 20 identical balls be distributed into 4 distinct boxes subject to
the following conditions:

Each box gets an even number of balls

Answer 1

there are 10 even numbers : 2,4,6,8,10,12,14,16,18,20
so, to get an even number each box : it should be 10P4
= 10!/(10-4)!
= ...

Answer 2

we are not permuting though

Answer 3

the correct answer is 286, i need to know how to achieve this -_-