I am using Mathcad Prime 3.1 and I can not find the minimum or maximum of functions at certain constraints.
As written your three constraints don't form a closed space (turn the inequalities into equals and plot:
If you invert the third constraint, the possible set closes, and the problem solves
This solution is not good, because the result is incorrect. The right side of inequality representing the production limitations and should not be changed. The real solution is the following figure.
Ah-hah!
Your original post was missing two constraints:
Without the additional restrictions that the values had to be GE 0,
the problem was unbounded
These two limitations I added later on, to close the space between so that I was able to get the solution to the equation.