,We have the next information
slope=-3
point=(1,-5)=
First, we will use the point-slope form

where m is the slope and (x1,y1) is a point where the line passes through
(x1,y1)=(1, -5)
m=-3
we substitute the values

then in order to obtain the slope-intercept form we isolate the y

the slope-intercept form is

the equation of the line in slope-intercept form is y=-3x-2