I am having troubles in solving correctly the following problem:
A company wants to minimize its total costs, on the condition that the income obtained from the sale of the quantities $x_1, x_2$ of the two products it produces exceed a certain minimum threshold. Knowing that the unit costs of manufacturing each good are linear functions of the produced outputs in the form $C_1 = x_1, C_2 = 2x_2$, that everything that is produced is sold and that the sale prices of the products are: $p_1 = 1$ and $p_2 = 3$, respectively. Determine the quantities $x_1, x_2$ that minimize the cost of the process.
$x_1 = 6/11$
$x_2 = 9/11$
$\lambda = -12/11$
$TotalCost(x_1,x_2) = 18/11$
I tried to solve it through the common way: using Lagrange function with Kuhn-Tucker conditions. However, I cannot reach the correct solution, despite I tried several times. I think I am not building Lagrange function correctly as a consequence of not understanding properly the economical meaning of what the problem want me to solve.
So I would be really greateful if you can help me to understand how to reach the correct solution to this specific problem, knowing that clarifying how to build Lagrange function and its restrictions is probably what it is needed here to fully understand the problem and its solution.