He assumed that you already know the properties of logarithms, which he posted not a long time ago in a previous thread of yours.
http://www.mathhelpforum.com/math-he...779-post3.html
When you have a difference between two logs, the two logs can be combined in one log of a quotient. The numerator contains the inside terms of the positive log and the denominator consists of the inside terms of the negative log.