Question

what is the slope of the line through the points (–3, 5) and (4, 5)

Answer 1

(y-y0)/(x-x0)=slope
it doesnt matter which point is which as long it has the same order in the 'y's and 'x's 
so the answer should be 0. because 5-5=0

Answer 2

Slope is referred to as m in y=my+b form and m=y2-y1/x2-x1
In this particular problem with the given coordinate points of (-3,5),(4,5) your numerator(or y2-y1 value) will be 0 and 0 divided by any real number is 0, so the the slope is zero.

You can visualize this as a straight line going through the y intercept at y=5

Hope this helps understand!