freight for products an numbers in categorys

[filou42]

Hello, i have this problem:
a.) One category with different products (cosmetics) : I need one freightprice , buy if someone buys more than 500€ = shipment gratis
b.) Other category with different products (tubes): 1-24 tubos = 20,-Euros freight / 25 tubes = no freight / 26 tubes = 20 Euros freight (the idea is, a complete carton with 25 tubes = freight gratis. An incomplete carton with 19 or 24 tubes = 20 Euros freight.

For example, if someone buys 50 tubes (16 tubes of ref.1 and 34 tubes of Ref.2) the shipment is for free. But if he buys 53 tubes (16 tubes of Ref.1 and 37x of Ref.2) = 20 Euros freight (2 complete cartons / 1 incomplete carton).

Anybody can solve me the problem? Is there any modul or a kind of configuration, that me let solve this problem?

Thanks and best regards
Filou