Question

Select the pair of equations whose graphs are perpendicular.

Answer 1

You know that 2 lines are perpendicular when the fulfil
m1*m2 = -1 
from D.)

m1 = -3/2
m2 = 2/3
so
m1*m2 = -3/2*2/3 = -1
this conclude that they are perpendicular each other

Answer 2

D. The lines intersect to form perpendicular.