Simple Question Regarding Shipping by Quantatity

[Scotty501]

Hi All,

Just about ready to go live with my online store. However, cant get my head round the shipping - despite reading the Wiki.

I am selling vinyl records, and I want to set the shipping by size of the record and then add a cost for every additonal record bought. Example

Category A (7" Vinyl) £3.99 for first item, plus £0.50p for every additional 7"
Category B (10" Vinyl) 4.29 for first item, plus 50p for every additional 10"
Category C etc
Category D

and so on. How would I do this? Also - what if the customer a 7" and 2 x 10" - would it use £3.99 + £4.29 plus £0.50p x two?