Final answer:
A 32-bit OS cannot use more than 4 GB of memory. Mary should upgrade her system to the 64-bit version of Windows 7 Professional.
Step-by-step explanation:
The problem is that a 32-bit operating system, such as Windows 7 Professional, can only utilize a maximum of 4 GB of memory. Therefore, even if Mary installs an additional 2 GB of memory, the operating system will not be able to use it. To solve this problem, Mary should upgrade her system to the 64-bit version of Windows 7 Professional. The 64-bit version can support more than 4 GB of memory and will allow Mary to take full advantage of the additional memory she has installed.