Question 1071480
Use this helpful example:
<a href="https://www.youtube.com/watch?v=VDKztVZUgnM">Equation of a line with two given points - example</a>


More focused on what you asked,  Slope means vertical change divided by horizontal change, and that VALUE is given in the problem description.  You have also a given point, and any unknown variable point on the line.


m for slope,

{{{m=(y-y[o])/(x-x[o])}}}


and if you just substitute the given values,
{{{-2=(y-(-5))/(x-(-7))}}}

{{{-2=(y+5)/(x+7)}}}

{{{-2(x+7)=y+5}}}


{{{y+5=-2x-14}}}


{{{y=-2x-14-5}}}


{{{highlight(y=-2x-19)}}}

The slope m, was already given in the problem description.  The y-intercept is  (0,-19).  
{{{highlight(b=-19)}}}
(You showed your general equation model as y=mx+b, and NOT as y=mx+B).