How would i find the sum of the infinite series: 1/3+2/9+4/

Charlie is a car salesman he earns $800 plus a 9% commission on all of her sales for the week if charlie receive the payment for $1960 this week how much where is total sales

Stephen thublin invests $1,000,000 in a 45-day certificate of deposit with 6.55% interest. what is the total interest income from the investment?

How is working backward similar to solving an equation?