I have two parallel lines in which the slopes of the line are just equal. But the only thing is Line 2 is bigger than Line 1

Line 1 (30,78) (19,41)

Line 2 (51,99) ( 25,20)

I want to know if LINE 1 passes through Y1 and Y2 of Line1. In this case Y1 of Line 1 =78 and Y2 of Line 1 =41 Please give me the equation or the algorithm.

I know that it passes but how to find it by an equation. Please advice. I'm not a math expert. Please explain me in a way that I understand. Give it to me in step by steps.

Thanks