6. Line a: y - 3x = 4
Line b: y = 3x + 5
Line c: y - 4x = 3

Which lines are parallel

for ex: the reciprocal of 3/4 is 4/3. it is the opposite.

reciprocal definition:

a mathematical expression or function so related to another that their product is one; the quantity obtained by dividing the number one by a given quantity.

true? is that what you're asking or do you mean something else?