Hey there!
The formula for slope is:
(second y value - first y value) divided by (second x value - first value).
So we can solve in the reverse and plug in what we know to find the missing point, k.
(-1 - -4 = 3) / (k - 4) =3/4
Since the top value comes out as 3, that means we have to find out what value k has to be so that the bottom part of the fraction will equal 4, this number would be 8. (8,-1)
Your value of k is 8.
Hope this helps. :)