Price List Lookups And Additonal Calculations For Out Of Range Values

The sheet has a price list (I attached the sheet). its a width x height(drop) format. If width or height <= minimum width/height then use the minimum listed. if width or height > minimum <=maximum then lookup in table next heightest value. here is the complication. any oversized items are priced as roundup((size -biggest size) / (biggest - second biggest size),0) * ( price of biggest-price of second biggest). so if my widths are

4600 4700 4800
10 25 35

and I am pricing 5050 I would do :-

calculate howmuch its oversize

5050-4800 = 250

Calculate the difference in the last 2 sizes

4800-4700 = 100

Calculate the rounded up multiples

250/100=2.5 rounded up = 3...........