The slopes of lines perpendicular to each other are opposite reciprocals. So, if you are given that the slope of a line is 3 and need to find the slope of a line perpendicular to that line, you'd flip that number around and negate it, leaving you with -1/3.
To find the slope of the given line, first get it into slope-intercept form (y - mx + b, where m is the slope and b is the y-intercept).
3y = -4x + 2 y = -4/3x + 2/3
The slope is -4/3. To find the slope of a perpendicular line, find its opposite reciprocal. It is 3/4.
The total repair cost for each store is the cost of repairs added to the sales tax. The amount of money saved will be the difference between the two total costs.
