Anewspaper sells both paper and digital subscriptions. the newspaper reports that 1,800 total subscriptions were sold last month and the total revenue from those subscription sales was $20,760. the digital subscriptions, d, cost $8 a month, and the paper subscriptions, p, cost $20 a month. which of the following systems of equations could be used to solve for the number of each type of subscription that was sold by the newspaper last month?