Provided their handwriting is neat enough, OneNote should be able to recognize the equations and convert them to text, which allows the equation solver to work its magic.

Discover Microsoft's Copilot in OneNote, an AI that transforms handwritten ink notes into summaries, tasks, and editable text using touch, pen, or mouse. Accessible via ribbon or dropdown ...

The optical character recognition (OCR) software supplied with many scanners is next to useless with handwriting, no matter how neat it is, but there is another option.