need help to solve this

Ím trying to get excel to solve this for me!
I have a small table that can look something loke this!


box type # - min kg - max kg
4 - 20 - 110
5 - 20 - 80
6 - 300 - 500

then i want to be able to distribute total weight among boxes

example:
I have a total weight of 1000 kg
I have two number 6 boxes
I have one number 4 box and
I have one number 5 box

So I want excel to disibute the wiegth among all boxes
solution:
-----------------------
box 6 = 450
box 6 = 410
box 5 = 60
box 4 = 80
-----------------------
total 1000 kg
-----------------------

I've been trying to use vlookup and randbetween

need help to compleat this.

You've only given us one constraint, i.e. the mass of the material going into your boxes. If this is all that matters, why not put 500 lbs in each of the large boxes?

no i need to put some weight in all boxes