Two parallel lines have the same gradient so the parallel line has the equation y=-5x+a.
We can find a, a constant, by plugging in the given point or we can use the form y-Y=-5(x-X) where (X,Y) is a point on the required line.
First, use y=-5x+a, -1=20+a, so a=-21 and y=-5x-21.
Now using (-4,-1) as (X,Y), the second form y+1=-5(x+4), which makes y=-5x-21, the same equation.