This particular exercise baffled me, but for a different reason this time
The verbiage of the question states "You can check Chapter 6 for StringBuffer methods that will help with this." so I took it literally to mean that the only methods that applied to the exercise were the ones discussed in the StringBuffer/StringBuilder section in chapter 6.
The charAt() and setCharAt() methods were never discussed in the context of StringBuffers/StringBuilders in Chapter 6. [ June 20, 2007: Message edited by: Brad Clarke ]