Answer:
$1200
Explanation:
Every month, Kiersten receives a subscription fee of $10 from each of the subscribers to her website.
Last month she had 100 subscribers. This month, 30 new subscribers joined and 10 members canceled their subscription. The amount of subscribers she has now is:
100 + 30 - 10 = 120
This means that this month, Kiersten will earn:
10 * 120 = $1200