Use curved arrows to show the movement of electrons in the following E2 mechanism. Draw the structure of the transition state.

It is a one-step elimination process where the proton and the leaving group are in a syn-antiperiplanar position.

In this reaction, a single concerted step is followed where proton abstraction and removal of the leaving group take place simultaneously.

The rate of the reaction depends upon both the base and the reactant. Hence they are considered to be bimolecular elimination reactions.

The base used here is ethoxide which is considered a strong base due to the localized electronic charge over the oxygen atom and electron-rich due to the +I effect of the ethyl group. Hence, they abstract protons followed by elimination.

The abstracted hydrogens are considered to be the $\text{β}$hydrogens as they are the first key part of elimination.

Representation of hydrogens

That $\text{β}$hydrogen is considered where the major elimination product formed is found to be more substituted.

Hence, observing all the steps, the following mechanism is considered

Mechanistic approach for the formation of products

The side products obtained are ethyl alcohol and bromide ion.