Answer:
$7.38
Explanation:
Let's start out with variable x, representing his original $286
y will represent his balance after his order ($182.06)
a is our variable for our one-time $8 shipping fee
b will represent the cost of one card
our equation is => ((x - a) - y) ÷ 13 = b
Substitute => ((286 - 8) - 182.06) ÷ 13 = b
Solve => (278 - 182.06) ÷ 13 = b
95.94 ÷ 13 = b
b = 7.38
Thus, our answer is $7.38 per card