What tool do you have to solve linear programming problems?

Is this just an issue with understanding how the equations and variables in the stated problem are represented in the tool you use to solve them?

In this problem the *objective* function is on the top line, expressed in 4 variables. The *constraints* are the 6 numbered equations.

Once you have an initial solution, the questions can be answered by changing the limits and coefficients. For example, in a), replace 3400, the current limit in [4], by 4000 and re-solve. Does that have any effect on the decision variables (x1 -> x4) in the solution? If so, then it will change the value of the objective function. If it has no effect, then the initial value of 3400 wasn't, in fact, limiting.