In the particular example you show, I think I would treat this as a main item with subdivisions. So the original statement would be 1/5 and each of the two sentences below would start in 3 with any runovers in 5. If you decide to treat this as a statement with displayed items, the statement would be 1/3 and the displayed items would be 5/7.
Is this taken from a math or science book that is done in Nemeth? I agree that this should be main item with subdivisions and may be treated as if the two Give ... statements had identifiers like a) and b).
The reason I asked about displayed is because I have a math book with displayed sentences that are not math expressions. "Application of the Formats Guidelines 2011 to Nemeth Transcriptions" says to follow Formats for displayed literary text, so I assume there will be a blank line before and after even though the book is brailled in Nemeth. (See attached example.)
You are correct that you would leave a blank line before and after displayed "literary" text as shown in your example. I think, however, that your original example is not of displayed text. Those kinds of decisions are left to the transcriber, so just be consistent in your interpretations.