Minimizing cost with restriction

[pede]

I have a problem with the following. I have to minimize cost, but I don't understand how i get solver to do it for me. Document attached should illustrate what i'm trying to do. Minimizing cost.xlsx

I have described my problem further in there.

Thanks in advance.

[shg]

See the Solver model in the attachment.

[pede]

Thanks for the brilliant answer. I've just solved it myself. But thanks so much for the help.