This video tells you how to find a slope of a parallel / perpendicular to it. In the equation y = mx + c, m is the slope. To calculate the slope of a line that is parallel to another line, you have to consider the rule m1 = m2 which means slope of the first line m1 is equal to the second line m2, if both the lines are parallel. Take the equation y = 2/3x - 7.2/3 is the slope. According to the rule m1 = 2/3 and so m2 = 2/3.Now to calculate the slope of perpendicular line you have another rule which says m2 = -1/m1.The slope of m2 is the negative reciprocal of m1.For example, take the equation y = -3/4 + 2.m1 = -3/4.Therefore m2 = + 4/3.Always right the rules as justification for full marks.