You have 440 kgs of wheat but you need to know how many grams that is. To get the answer multiply by 1000 which gives you 440000 grams.

In 180 kgs of onions there are 180000 grams, to achieve this take 180 and just multiply by 1000.

How many grams of rye are there in 270 kgs? Just multiply by 1000 to get the answer of 270000 grams.

You've got 790 kgs of barley but someone only wants to buy that in units of grams, to change the units multiply by 1000. Now you have 790000 grams.