A new clothing store uses advertising through social media to draw customers and increase the number of transactions each month. The number of transactions, f(n), for n months is shown in the table below. Month, n No. of Transactions, f(n) 1 10 2 20 3 40 4 80 If the number of transactions per month continues to increase in this way, fill in the values for a and r to create the function that describes this situation.