The two lines are said to be perpendicular if the product of thier slope is equal to the -1
The general equation of line:

where, m is the slope of the line
The given expression : y - 5 = -3(x -1 )
Simplify the expression:

Slope of the given line is m = (-3)
Let the slope of the second line is n
From the condition of the perpendicular lines

Slope of the second line which is perpendicular to the given line is 1/3
Use the general form of equation of line to get the expression pf line2:
The passing points : (1,5)

The equation of line which is perpendicular to the line y-5=-3(x-1) is y - 5 = 1/3 (x - 1 )
Answer : y - 5 = 1/3 (x - 1 )