It would be good practice to write the structures form these names. The name given in your text for this alkene illustrates the rule that the longest chain you count must include the double bond. The longest chain of carbons in the molecule is actually 8, but the longest chain including the double bond is only 6, thus this is named as a hexene. Be sure you do these two problems. Do this problem.
Answer is in the text.
See page 378 Figure 12.3 for what occurs. 12.21 Think addition polymers . This is 2-methylpropene. Only one product is possible when bromine is added to the double bond. This happens because the carbocation formed when the two electrons in the pi bond attach to the hydrogen ion will be a tertiary carbocation.