Since there is no feasible region defined, there is no answer possible.
It would depend on the feasible region.
Since x and y can get smaller and smaller without a limit, there is no minimum for the value of 3x+3y.
Unfortunately, limitations of the browser used by Answers.com means that we cannot see most symbols. It is therefore impossible to give a proper answer to your question. Please resubmit your question spelling out the symbols as "plus", "minus", "equals", "squared", "cubed" etc. There is no visible operator between 3x4y unless some of them are meant to be powers. Also, it is necessary to know the feasible region. But since you have not bothered to provide that information, I cannot provide a sensible answer.
(1/x) + (1/y) + (1/z) is a minimum value when x=y=z=10. Symmetry gives either maximum or minimum value.
Since there is no feasible region defined, there is no answer possible.
It is 18.
2x+2y
The answer depends on the feasible region and there is no information on which to determine that.
It is 18.
It would depend on the feasible region.
42
maximum value of 6y+10y
(6x)(5y)
14
The answer obviously depends on what the boundaries of the feasibility region are.
78