How to find tip-age of a bill, you move the decimal point of the percentage 2 to the left. So now instead of 15%, you have 0.15. When you arrange the sentence like this, what is 15% of 85, you automatically know that you are multiplying, because "of" will translate into multiply. With your numbers, the formula would be (0.15×85)+85=total. Using the order of operations, you would get 12.75+85=97.75
