Answer:
200 dollars,
I am assuming that your question goes like this: "Kiersten runs a website that helps people learn programming. Every month, Kiersten reveives a subscription fee of $10, $10 from each of the subscribers to her website. Last month, the website had 100 subscribers. This month, 30 new members joined the website, and 10 members cancelled their subscription. How much money will Kiersten's online business earn this month?
Explanation:
Since her website had 100 subscribers last month, she earned $1000 (100 x 10). This month, 30 members joined and 10 members left, so in total, she gained 20 subscribers for a total of 120 subscribers this month. So she made 1200 dollars this month (100 x 120). She earned 200 more dollars this month since 1200-1000=20.