Since y = 7x - 9 is in slope-intercept form, its slope is 7. Since parallel lines have the same slope, the slope of the new line will also be 7. m = 7. b = 3. Thus, the equation of the line is y = 7x + 3. Example 4: Write an equation of the line with y-intercept 4 that is perpendicular to the line 3y - x = 9. The slope of 3y - x = 9 is . If you know the slope of a line and a point on the line, you can draw a graph. So using an equation in the point-slope form, you can easily identify the slope and a point. Consider the equation . You can tell from this equation that the y-intercept is at (0, −1). Start by plotting that point, (0, −1), on a graph.