Explanation:
Hey there!
The equation is; y= -3x
or, 3x+y = 0.......... (I)
From equation (I)


Therefore, m= -3
Now, As per the condition of perpendicular lines;
M1*M2 = -1
-3*M2 = -1
M2= -1/-3
Therefore, the slope of a line which is perpendicular to the equation is; 1/3.
Hope it helps...