Really that’s your question :> the answer is 5
Factor 16 and see the - factor pairs and add them, see which add to -12
-1-16=-17 nope
-2-8=-10 nope
-4-4=-8
hmm
we will solve with math
xy=16
x+y=-12
minus x both sides
y=-12-x
sub for y in other equation
x(-12-x)=16
-12x-x^2=16
add 12x+x^2 both sides
0=x^2+12x+16
use quadratic formula
if you have
ax^2+bx+c=0
x=

0=x^2+12x+16
a=1
b=12
c=16
x=

x=

x=

x=

x=

x=

or

aprox
x=-1.52786 or -10.4721
those are the numbers
the numbes are -1.52786 or -10.4721
We can use the points in either order and you will still get the same slope. I usually solve in order that is given. So the first coordinates I label (x1,y1) and the second is (x2,y2).
Slope=m=(y2-y1)/(x2-x1)
m=(9-5)/(3-1)=4/2=2
Slope is 2.