To find the sales tax multiply the purchase price by the sales tax rate. Remember to convert the sales tax rate from a percent to a decimal number. Once the sales tax is calculated, it is added to the purchase price. The result is the total cost—this is what the customer pays.
I know for a positive fact that there's a picture in the book that goes along with this question. I know that because the question talks about machines that are "shown at the right".
What you have to understand is the reason for the picture. It's expensive to print pictures in books, and if the picture were not necessary, then it wouldn't be printed there.
It IS necessary, because you can't solve the problem, or even understand it, without the picture. And that's why nobody here will be able to answer this question for you. We don't even know what the two functions are, and those make a BIG difference ! !