The line y = -3 is a horizontal line. The perpendicular line will be vertical, so will have an equation of the form
x = c
for some constant c.
You want the vertical line to go through the point (4, -6), so the required value of c is the x-value of that point: 4
Your equation is
x = 4
x = c
for some constant c.
You want the vertical line to go through the point (4, -6), so the required value of c is the x-value of that point: 4
Your equation is
x = 4