Question

Lok

Answer 1

Why do you want to use equations??? Just think. Obviously you want to invest as much as possible in the 6% investment. But you have to invest at least 1/3 in Type A unfortunately.
So put 1/3 of your investment (or 200 000) in Type A and 2/3 of your investment (or 400 000) in Type B.

Answer 2

Because I need to somehow prove it in a graph and find what the optimal amounts are that should be put in each investment.