Ah... yeah, the books aren't a big help sometimes with problems like these... they only show you one way to deal with them usually... [And sometimes even then it's not easy to tell.] I'll go through one of 'em.

[He proceeds to walk her through one of the problems, showing her step-by-step how the equation and process to the solution work, and then checks his work by plugging the numbers back in - it's correct.] Does that make it a little easier?