I will give you a hint,
whenever an equation is perendicular, it has the NEGATIVE RECIPROCAL of the original slope.
This is an example problem:
y = 2x + 9 and passes through ( 4, 2)?
So new slope is 2 => -1/2
y = -1/2x + b
2 = -4/2 + b (Plug in coordinates (4, 2)
4 = b
So the equation is y = -1/2x + 4