The slope-intercept form:
[tex]y=mx+b[/tex]
m - slope
b - y-intercept
We have the slope
[tex]m=-2\to y=-2x+b[/tex]
Put the coordinates of the point (-1, 5) to the equation of the line:
[tex]5=-2(-1)+b[/tex]
[tex]5=2+b[/tex] subtract 2 from both sides
[tex]3=b\to b=3[/tex]
Answer: [tex]y=-2x+3[/tex]