A pair of perpendicular lines would be line CF and line AJ.
Line BC and line AJ are NOT perpendicular because when a pair of lines are perpendicular, all angles become 90 degrees. It is obvious, in the case, if you were to slide line BC on top of line AJ, the angles will not equal 90 degrees.
20%, just calculate the fraction of mystery books and multiply that by 100 %
Skip counting 3and rule is adding 3
Answer:

- Please see the attached picture for full solution!:)
----------------- HappY LearninG <3 --------------