Using the point slope form y - y1 = m(x-x1)
m is the slope, because the lines are parallel the slope is identical, so m = -2.
Replace x1 and y1 with the given point and then solve for y:
y - 1 = -2(x-4)
Simplify:
y - 1 = -2x + 8
Add 1 to both sides:
y = -2x +9
