I believe your question may be better suited for the UEB category of the Ask an Expert forum.
In response to your question, since your example fraction is not entirely numeric (section 6.1 in the Guidelines for Technical Material), you should use the general fraction indicators (section 6.4 in the GTM). And, since your minus/negative signs are not in the superscript position, you should simply use the minus symbol (section 3.4 of the GTM)
The following is how I would transcribe your sample fraction (simbraille image attached):
[The grade 1 symbol indicator is used before the opening general fraction indicator so that it is not misread as the "of" contraction. No other grade 1 indicators are used because 1) the minus symbol cannot be misread, and 2) the first numeric indicator sets grade 1 mode.]
The GTM (UEB Guidelines for Technical Material) can be found through BANA's website.
This reply was modified 6 years, 11 months ago by kdejute.