Although 70 percent of adult smokers in the united states want to quit smoking, and up to 44 percent make a serious attempt to quit each year, how many actually succeed?

Let us consider this situation as 100 adult people who smoke in the United states.
Then, 70 percent of 100 want to quit smoking i.e. 70 people out of 100 adult smokers want to quit smoking. 
Now, 44 percent of 70 people actually make an attempt to succeed. Means at most 44% of 70 people succeed. i.e.  = 30.8

I.e maximum 30 people out of 70 are able to quit smoking in the United states. This  count can be less as well but the maximum number is 30.