If you find Goal Seek useful, but you need more power, you'll want to download and use Solver for Excel for Mac 2011. Solver is a free add-in that lets you change multiple variables, which enables you to ask more complex questions of your data.
To download and install Solver for Excel for Mac 2011, follow these steps:
Solver.pkgfile you downloaded to launch the Install Solver application, and then follow through its steps. Install Solver uses a standard installation ...