Hi needs some help !!!

I am trying to create a very simple formula to calculate the courier shipping charge. " but i am just a nuts and needs help "

i just want the formula to automatically calculate the shipping cost for me each time when i key in the " weight "

The standard formula to calculate the courier shipping charge are in this way.

1) There is a initial minimum charge. first " 0.1kg to 0.5kg " was charge at the price of $24.80. and thereafter for every addintional 0.5kg will be additional charge $5.80 ( Which mean the charger of 1kg is [$24.80 + $5.80= $30.60 )

Any help will be greatly appreciated!

Thanks !