This Instructional Activity is a part of the Lesson 19, Unit 2, Grade 7.Generate a classroom discussion about a new concept-the concept of sales tax. Discuss what it is, the purpose of it, and how it is calculated. Once students have a general understanding that sales tax is a number added to the cost of an item, and it is found by finding the sales rate of the item and added to the cost, lead students through the second chart, which is an extension of the first.