Final answer:
The number of rentals where the cost is the same for both Amazon and Redbox in a one-month time period is 20 rentals.
Step-by-step explanation:
To find the number of rentals at which the cost will be the same for both Amazon and Redbox, we need to set up an equation. Let's say the cost of renting from Amazon is $A and the cost of renting from Redbox is $R. In a one-month time period, the total cost for renting from Amazon will be 5A, 10A, 15A, or 20A depending on the number of rentals. Similarly, the total cost for renting from Redbox will be 5R, 10R, 15R, or 20R. We want to find the number of rentals where 5A is equal to 5R, 10A is equal to 10R, and so on. It turns out that this happens when the number of rentals is the same. Therefore, the answer is d. 20 rentals.