Profit calculator

hello

can anyone point me in the right direction? searched google but no luck
what i need:

a profit calculator to:
Ex: people can calculate their profit for selling stuff.
Number of people: 20
Number of dvds: 10
Number of books: 10

Total profit 12000$

now here is the math: when they add 10 dvds this will be multiplied with 32$
when they add 10 books it will be multiplied with 28$
so 3210=320$+280$(1028)=600$ * 20people=12000$

Can someone tell me?thanks