We're given a point that the line intersects and its slope.
Let's use Point-slope:-
[tex]\boxed{y-y1=m(x-x1)}[/tex]
y1 = -5
m=-5
x1=-1
[tex]\boxed{y-(-5)=-5(x-(-1)}[/tex]
[tex]\boxed{y+5=-5(x+1)}[/tex]
Convert to slope-intercept:-
[tex]\boxed{y+5=-5x-5}[/tex]
[tex]\boxed{y=-5x-5-5}[/tex]
Finally,
[tex]\bigstar{\boxed{\pmb{y=-5x-10}}[/tex]
Hope everything is clear; if you need any clarification/explanation, kindly let me know, and I will comment and/or edit my answer :)