I believe the answer to the question is D.
Let us find the slopes of the two lines
ax+by=c, slope m1 = -a/b
bx-ay=c, slope m2 = b/a
m1*m2 = (-a/b)(b/a) = -1
Therefore the two lines are perpendicular so the answer is D
-0.03125 this would be the answer to that problem
