Question

-12-13/-1-4
how is it -5 it said this is the right answer (-5) for the y2-y1/x2-x1 thingamajigi

Answer 1

Trying to decompose what you are showing, I will assume you are finding
the slope between the points (-1 ,-12) and (4,13)

It would be ....
slope = (-12-13) / (-1-4)
= -25/-5
= 5

Notice how critical those brackets are ?
your expression would be
-12-13/-1-4
= -12 + 13 - 4
= -3
https://www.wolframalpha.com/input/?i=-12-13%2F-1-4