The slope-intercept form:
[tex]y=mx+b[/tex]
m - slope (a rate of change)
b - y-intercept
We have the slope [tex]m=-3\to y=-3x+b[/tex]
and point (3, -5). Substitute:
[tex]-5=-3(3)+b[/tex]
[tex]-5=-9+b[/tex] add 9 to both sides
[tex]4=b\to b=4[/tex]
Answer: [tex]y=-3x+4[/tex]