Lines m and p are perpendicular. if the slope of line m is -3 what is the slope of line p

For two lines to be perpendicular, their slopes must be negative reciprocals of one another, mathematically:

m1*m2=-1, in this case our reference line has a slope of -3 so:

-3m=-1  divide both sides by -3

m=-1/-3

m=1/3

So the perpendicular line will have a slope of 1/3

What am i doing here. add?