How is math involved in fashion designing?

i need to make 400 jackets for my store. my material from star to finish cost me 30p a metre. i have 1600 metres made. shipping the jacket is £30.00 a kilo from India to England. each jacket weights 0.9kg. and the total labour for each jacket to be made is 45p. how much do i need to pay?( this is not a real example). now do i prove my point!