Question 446851
Y=mX+b
V=nU+c
b and c are not important because lines continues and in 2D two line are:
1)	Parallel (example y=2x and 2 y=4x+3)
Or
2)	Coincident (example y=2x+5 and 2y=4x+10)
And or 
3)	Crisscross (any lines that are not parallel an coincident)
Only the position is that in one lines x greats also y greats and other line x greats y reduces and two (growth and reduction) are equal absolute value. There multiple slopes are -1.

Slop y=mx+b with permits  m=(-1)/5 is (-1)/5.
Slop two lines that are perpendicular together follow this formula:
m×n=-1
That m and n are slopes the lines.
There for the answer is (+5) because (-1/5)×(+5)=-1