The answer is y = -1/5x + 5
Perpendicular means the opposite reciprocal of the slope. The reciprocal of 5 would be 1/5. The opposite sign would be negative, so -1/5.
The equation that you use is y - y1 = m(x - x1)
The point is (-15,8).
x1 = -15
y1= 8
m= -1/5
y - 8 = -1/5(x - (-15)).
The 15 becomes positive.
y - 8 = -1/5(x+15)
Distribute
y - 8 = -1/5x - 3
Add 8 to both sides
y = -1/5x + 5