[Urgent!] Weights Question... (kg - Tonnes)

Basically its rather simple to exmplain, getting the answer is the hard part!!! but i do request urgent help!

I know the following information:

The total number of Pallets = 572

The weight of the pallet = 18 kg /each

There is 90,428 boxes

The weight of a box = 20g /box

**So my question is, **

From the following information how can i work out in tonnes how much cardboard (boxes) have been used?!?

**But the tricky part is, i know the answer is a rounded number of 3! **

I need to know how we got to that answer...

Please help me. Its Friday and im Blonde.. so things aint going too well!

Thank you,

Nec. x