I can write an equation

Answer: y = -x + 2
Step-by-step explanation:
If you are familliar with the point-slope form this is very helpful
Point-slope:
[tex]y-y_1=m(x-x_1)[/tex]
Plug in our values of [tex]m = -1, y_1=-1,x_1=3[/tex] to get:
[tex]y-(-1) = -1(x-3)[/tex]
Simplify
[tex]y+1=-x+3[/tex]
[tex]y=-x+2[/tex]