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

There are tough problems that every business faces, and they can slow things down, make budgets stretch, or put off decisions ...

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).