to get minimum cost

Problem statement
Input: market size, MRP, required size, required qty,
Output: minimum cost, which market size and how many sheet used with minimum wastage
For example given is
Market Size
Market size MRP Required size Required QTY
8 105 2.13 7
10 115 4.39 29
12 130 7.94 4
13.5 140 7.21 15
15 150

What I have tried is as follows
Have the total required qty
So I have to work out with market size sheets to get minimum wastage of the market size sheets
I have made the combination of the required qty which I have 19201 records
Now I have taken the closes total range of available market size i.e. from above records I have taken records coming in range say 6 to 8 which is more closes to 8
Likewise I have take the combination I have reduce the records to say count of required qty
Then I have put the efforts to combine the required qty to make in 1 available market size sheet
But now I am not sure that the solution is best & cheap
Can any body help
I want to get minimum cost output with less wastage of available market size