Interpretation of the variance of a slope is unclear because the OP seems to be confused by notation, and therefore the notation in the question is confusing. StatStudent pointed this out in the comments, and suggested (correctly in my opinion) that the question could be answered by resolving this confusion.
I went ahead and edited the notation to better reflect what StatStudent (and I) thought the OP meant, but then had second thoughts.
What's the right thing to do here? I'm torn between making the question clear to future readers, but potentially making the answers and comments confusing, or leaving the question confusing (and maybe harder to find by searching) but then having the answers correspond better to the question as it was asked.