Gina paints beach scenes on notecards. she sells packages of 8 notecards for $8 for one package, $16 for 2 packages, and $24 for 3 packages. which equation is the rule for the pattern if n is the number of packages and d is the selling price in dollars?

In this question, each package has 8 notecards. 
one notecard costs $8
2 notecards cost $16
3 notecards cost $24
if n - number of packages
d - selling price in dollars
We can see that with each additional notecard bought the cost increases by $8
therefore there's a proportional relationship between n and d
As n increases, d increases by the same amount.
if we put it in an equation,
d = 8*n
n - 1 package and d is 8 
if n - 2
d = 8*2
d = 16
Therefore we can use the following equation;
d=8n