Thank you for the question and the sample file.
You're right that the expressions should be brailled all in Nemeth, because the words are as much a part of the math as are the numbers.
Please see the attached BRF, noting the few differences from your sample, namely:
- abbreviation p. (for page) must be on the same braille line as its associated number (Nemeth Code XXV.195.c)
- comma following the word years within the first expression must be a literary comma (dot 2) (Nemeth Code VI.38.iv)
- abbreviation SD (for Standard Deviation) should be capitalized with the double capitalization indicator and not have its letters capitalized individually, because its letters do not have separate values
- opening Nemeth Code indicator should be placed after a blank cell on a line with the text that precedes the displayed material, because the displayed material spans more than one braille line
- the indention of the displayed material should be 3-5 (displayed to narrative text), with the Standard Deviation expressions treated as runovers and not separate expressions.