On Windows, Solver may be added in by going to File (in Excel 2007 it’s the top left Windows button) > Options > Add-ins, and under the Manage drop-down choosing Excel Add-ins and pressing the ...

Excel can solve for unknown variables, either for a single cell with Goal Seek or multiple cells with Solver.

The popular Solver for Excel add-on has been redeveloped for Excel 2008 by Frontline Systems and Microsoft.

Solver is a linear programming / analysis tool for Excel that was included with Excel 2004 as an add-in, but dropped from Excel 2008 since it required Visual Basic for Applications (VBA).