The equation for Line P can be rearranged into slope/intercept form as:
y = (5/6) x -4
Thus the slope of line P is 5/6. Since Line L is perpendicular to line P, its slope is - (6/5) . This is the negative reciprocal rule. Once the slope of Line L is known, the formula for a line with known slope and one known point comes into play. For Line L
(y-3) = -(6/5) ( x - (-4)) This can be rearranged as
y = -(6/5) x - 9/5
So the slope of Line L is -(6/5) and the y intercept is -9/5