unit conversion

let's start by converting all of these into grams. this way, it will be easier to put in order. 

1 kilogram = 1000 grams.

so, 7 kg would be 7000 grams, and 3 kg would be 3000 grams.

now, we have:

7000 grams

600 grams

100 grams

3000 grams

we can now order these from least to greatest, because they are all in the same unit.

the final order would be:

100 grams

600 grams

3000 grams

7000 grams

now we have to convert it back, to suit the original problem.

100 grams

600 grams

3 kg

7 kg

and we're done! hope this helped