The following utility will enable you to convert mass/weight expressed in hundredweight to tonnes
To convert hundredweight to tonnes divide by 19.68413
You've got 890 hundredweight of carrots but someone only wants to buy that in units of tonnes, to change the units divide by 19.68413. Now you have 45.21409 tonnes.
In 560 hundredweight of wheat there are 28.44931 tonnes, to achieve this take 560 and just divide by 19.68413.
To convert 390 hundredweight into tonnes divide by 19.68413 giving 19.81292 tonnes.