What is the purpose of writing a topic sentence

Quick computing currently sells 12 million computer chips each year at a price of $19 per chip. it is about to introduce a new chip, and it forecasts annual sales of 22 million of these improved chips at a price of $24 each. however, demand for the old chip will decrease, and sales of the old chip are expected to fall to 6 million per year. the old chips cost $10 each to manufacture, and the new ones will cost $14 each. what is the proper cash flow to use to evaluate the present value of the introduction of the new chip? (enter your answer in millions.)