Expanding on Phillip's reply. Solver is a singular add-in, it isn't the Analysis Toolpak.
Further, Solver is included with Office 2011 so there is no need to ' download' anything. If it isn't listed in the Tools menu or displayed in the Analysis group on the Data tab, go to Tools Add-Ins. Then check the box adjacent to the listing. Solver will be available when you OK out of the dialog. If you do mean the Analysis Toolpak, it is no longer supplied by Microsoft.
Note: If you are student of University of Kentucky you can download the software edition free. To do so you have to enter your Student ID and temporary passcode which is provided by University. After logging in you can opt for free Version of this software.
However, a comparable package is provided free of charge from as I understand it the same developer. Instructions for obtaining StatPlus:mac LE are available in Excel Help: Please mark HELPFUL or ANSWERED as appropriate to keep list as clean as possible ☺ Regards, Bob J.