Final answer:
The reaction can proceed via SN2, E2, or both mechanisms depending on the structure of the substrate. The bromine atom will serve as the leaving group.
Step-by-step explanation:
In determining whether the reaction will proceed via SN2 or E2 mechanism, the structure of the substrate and the solvent play important roles. SN2 reactions tend to occur on primary or methyl substrates, while E2 reactions occur on tertiary substrates. Both mechanisms can occur simultaneously on secondary substrates. The leaving group in this case would be the bromine atom.