7/8 & - 8/7 are these line slope perpendicular or parallel or neither

Perpendicular!

Step-by-step explanation:

If they were parallel they would have the exact same slope. If they are perpendicular their slopes would be opposite reciprocals of each other ... which they are. Another trick to tell if two slopes are perpendicular is to multiply them by each other and if the answer equals - 1 they are perpendicular:

7/8 • - 8/7 = - 1/1 = - 1