Susan,
Yes, you are correctly using the general fraction indicators with the general fraction line in a fraction that includes something other than digits, decimal points, commas or separator spaces. In Guidelines for Technical Material part 6.4, general fractions are discussed, and examples are given.
So, while ¼ would be transcribed: #a/d
A fraction like “question mark over 4” is not a simple numeric fraction and so is transcribed using the general fraction indicators and general fraction line:
;;(8./#d)
–Kyle