Consider the line x + 3y = - 9 What is the slope of a line parallel to this line? What is the slope of a line perpendicular to this line?

Hello ther is a solution:

x+3y = - 9

3y = - x-9

y = (-1/3) x-3

1) the slope of a line parallel to this line is : (-1/3)

2) let ' a ' the slope of a line perpendicular a line: x+3y = - 9

I'have (-1/3) * a = - 1

a = 3