I was given a problem on a ACT Prep course site that involved something called expectals. I've never heard of these before and I was hoping someone could either give me a break down of what to do to answer this problems or point me in the right direction to figure out how to work more problems like it.

http://www.mathhelpforum.com/math-he...-problems.html <- This is a link to a thread with the exact problem I was given. The problems are worked out but i don't fully understand what was done to get the answer. [It's the second question] Your help will be greatly appreciated. Thank you!