a. How does the first step in the reaction of ethene with Br2 differ from the first

Question:

a. How does the first step in the reaction of ethene with Br2 differ from the first step in the reaction of ethene with HBr?
b. To understand why Br- attacks a carbon atom of the bromonium ion rather than the positively charged bromine atom, draw the product that would be obtained if did attack the bromine atom.