A tutorial for installing the Solver add-in for Windows Excel can be found here.
Information on Excel Solver for the Mac can be found here.
If you have Mac Excel 2011, then Solver comes bundled with Excel, and you can add it in using the guide given on the website listed above. Unfortunately, there is a bug in the code which requires an alternative approach to adding in Solver. The alternative approach cannot be found anywhere on the web or in any official documentation. Here is the "trick" if you need it.
It is possible to check your answers using MatLab or R.