Ok i want a buy Now button on my website. Each item costs £45 for postage i want a standard rate of £15 per tin i also want the buyers to change the quantity they want. however here is when i get the problem. When i put the postage cost in (£15) thats just a flat rate. When the user then updates the quantity to say 2 Items (£90) i want the postage to be (£30) however the postage stays at £15 any1 who understands this could u help me and let me know how to do this