6.23 is another case of the problem in 6.3.  Try to understand the proofs in 6.3(a) and 6.3(b), and use a similar idea to 6.3(b) to work on 6.23.

6.24 is similar to 6.4.

In most chapters, there are the similarity between the practice problems and the example problems of corresponding problem numbers like the above.

For 6.28 and 6.30, they are not exactly similar to the problems 6.8 and 6.10.  One first thing to do for the problems is to draw the diagrams.  Interpret the question in an accurate diagram, and see what is known and what is to be found.  Some auxiliary lines could be added.  The general guidelines include: if two circles are tangent to each other, connect their centers (the line will pass through the tangent point); if one circle and one line are tangent, make a radius connecting the center and the tangent point (the radius is perpendicular to the given line).