You multiply the percentage and money for example.
100 dollar phone. The tax is 20%, you move the decimals two times to the left. (.20) then you multiply .20 and 100 to get the tax, which is 20. Now since you know the tax is 20 dollars, you add it to the amount of the item, so the total is 120 dollars.
To find the slope you use rise over run so you take one dot (2,-5) and go up 2 units so that it would get one the same line as the other dot (5,-3) and then go to the right 3 units to get you to the exact spot that the dot is
