For each other, the web site applies a 7.7% sales tax to the price of the cards, plus a one-time mailing fee of $5.95. Based on the information in the table, what will be the total cost for an order for 280?

To answer this question you will want to create an equation that you can use to find the final cost for any number of cards.

The first step is to find the relationship between the cost and the number of cards in the chart.  To do this you need to find a unit price per card.  To find this divide the price in any column by the number of cards you will get from the same row.

$13/20 = $0.65 per card.

Now you can set up the equation with the remaining information.

T = 1.077(0.65x) + 5.95
1.077 represents the total amount of the cards (1) plus sales tax (0.077)
x stands for the number of cards you will buy
one time charge of $5.95 is added on at the end

T = 1.077 (0.65 x 280) + 5.95
T = $201.96