Use the principles in How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly and Outline Numbering in Word for OS X - Brandwares Best Practices - Office Best Practices for your numbering.


This links your numbering to styles. Use the styles to set your numbering, not any buttons on the ribbon or toolbar.
Have the styles in both numbering schemes that you want followed by your a.b.c. body text set to use that style for the next paragraph. See Question and Answer Styles for an example of some styles set this way.