Cadbury wants to change their main ingredients with A and B.

There are four kinds of the ingredients per unit that has A and B:

Ingredients D1 D2 D3 D4

A 5 0 3 2

B 4 2 0 3

Cost/kg 12 4 6 13

Cadbury needs 7 units of A and 2 units of B every production batch.

Which type of ingredients and what amount should be purchased to provide the cheapest ingredients?