Algebra in Design Fundamentals Exam

As a teacher, you are collecting average grades for your class. The averages for the first three semesters are 93%, 87%, and 86% respectively. What is the minimum score needed to end the year with an overall average of 90%?

You are planning on ordering a bulk of tabloid paper. This company that you are ordering from has a progressive discount throughout the week; Monday the bulk is full price, Tuesday the bulk is 10% off of Monday's price, Wednesday the bulk is 20% off of Tuesday's Price, Thursday, the bulk is 15% off of Wednesday's price. Write a formula which represents the price on Thursday.