The Solver AddIn Utility for Excel 2013
When dealing with complex problems in Excel 2013, you might need to use the Solver addin. For example, use the Solver to find the best solution when you need to change multiple input values in your model and you need to impose constraints on these values and/or the output value.
The Solver addin works by applying iterative methods to find the “best” solution given the inputs, desired solution, and the constraints that you impose. With each iteration, the program applies a trialanderror method (based on the use of linear or nonlinear equations and inequalities) that attempts to get closer to the optimum solution.
When using the Solver addin, keep in mind that many problems, especially the more complicated ones, have many solutions. Although the Solver returns the optimum solution, given the starting values, the variables that can change, and the constraints that you define, this solution is often not the only one possible and, in fact, may not be the best solution for you.
To be sure that you are finding the best solution, you may want to run the Solver more than once, adjusting the initial values each time you solve the problem.
When setting up the problem for the Solver addin in your worksheet, define the following items:

Objective cell: The target cell in your worksheet whose value is to be maximized, minimized, or made to reach a particular value. Note that this cell must contain a formula.

Variable cells: The changing cells in your worksheet whose values are to be adjusted until the answer is found.

Constraint cells: The cells that contains the limits that you impose on the changing values in the variable cells and/or the target cell in the objective cell.
After you finish defining the problem with these parameters and have the Solver addin solve the problem, the program returns the optimum solution by modifying the values in your worksheet. At this point, you can choose to retain the changes in the worksheet or restore the original values to the worksheet. You can also save the solution as a scenario to view later before you restore the original values.
You can use the Solver addin with the Scenario Manager to help set up a problem to solve or to save a solution so that you can view it at a later date. The changing cells that you define for the Scenario Manager are automatically picked up and used by the Solver when you select this command, and vice versa.
Also, you can save the Solver’s solution to a problem as a scenario (by clicking the Save Scenario button in the Solver dialog box) that you can then view with the Scenario Manager.
Keep in mind that the Solver is an addin utility. This means that, before you can use it, you need to make sure that the Solver addin program is still loaded, as indicated by the appearance of the Solver button in the Analysis group at the end of the Data tab on the Ribbon.
If this button is missing, you can load Solver by opening the AddIns tab of the Excel Options dialog box (Alt+FTAA) and then clicking the Go button after making sure that Excel AddIns is displayed in the Manage dropdown list box to its immediate left.
Then, select the Solver Addin check box in the AddIns dialog box to put a check mark in it before you click OK to close the dialog box and reload the addin.