Two parallel lines are graphed on a coordinate plane. how many of the lines could represent proportional relationship? explain.

It's not necessary that either one represents a proportional
relationship.  But if either one does, then the other one doesn't. 
They can't both represent such a relationship.

The graph of a proportional relationship must go through
the origin.  If one of a pair of parallel lines goes through
the origin, then the other one doesn't. (If two parallel lines
both went through the origin, then they would both be the
same line.)

Distance=slopeslope is -2/4which equals-1/2the distance between these two points is -1/2