If you have edunuity, the answer is... Two parallel lines will have the same slope. The slopes of parallel lines have to be equal. The y-intercepts of those two lines have to be different, otherwise they would be the same line. The x-intercepts of the parallel lines would also be different.
The gradient would have to be the same in the two lines, as parallel lines are lines that will never touch and they can only do that with the sand gradient (which is the same as slope). The y-intercept would have to be different, as if they had the same slope and intercept, they wouldn't be two different lines anymore. I hope this helps!