$(5$ pts$.)$ Consider the following two dislocations in a face$-$centered cubic material:

$\frac{a}{6}[\frac{2}{b}ar(1)1]+\frac{a}{6}[\frac{1}{b}ar\frac{2}{b}ar(1)]?$

What is the new Burgers vector after their reaction? Would the reaction be energetically favorable?