Question

what must be true about angle 6 and angle 3 for the lines to be parallel? Name the postulate or therom

Answer 1

angle 6 and angle 3 are co-interior angles
theorem:If two parallel lines are cut by a transversal, then the pairs of consecutive interior angles formed are supplementary.

Answer 2

It should be supplementary angles theorem. 6 and 3 must add to 180 degrees to make a straight line.