Statement (1) is insufficient. We know the total amount she was charged, but not how much she was charged per month. It could be $10 per month for 12 months, or $120 per month for one month.

Statement (2) is also insufficient. This gives us a difference between what actually happened and a hypotetical, but even if it tells us something important, it doesn't give us any information about the length of the membership, such as the total amount she was charged.

Taken together, the statements are sufficient. (2) tells us that each month's membership fee was $30. If she had ended her membership 20 days sooner, that could result in two changes to her total membership fee: if she actually canceled on, say, the 25th of the month, then canceling 20 days sooner means her number of months was rounded up to the same number, and the charge was the same. If she canceled on, say, the 10th of the month, then canceling 20 days sooner means her number of months was rounded up to one less.

Since she would have been charged less, the first option is impossible: if her number of months didn't change, she would've been charged the same amount. So, her number of months would have changed by one, indicating that $30 less represents one month. (1) gives us the total amount of $120, so if the membership fee is $30 per month, she was charged for 4 months. Choice (C) is correct.