This exercise is designed with a couple of aims in mind.  Firstly, to provide some basic practice of evaluation of logarithms and secondly, to lead pupils into some key laws of logs.  

Question 16 offers pupils opportunity to generate their own examples and demonstrate/consolidate/develop a deep understanding of logarithms.

Question 18 provides an element of challenge, but is designed to help learners attend to the key underlying idea of logarithms as being connected with powers. 

credit:  @chrismcgrane84