Elimination reaction (especially -`beta`-elimination) are as common as the nucleophilic subsititution reaction in case of alkyl halides. Specify the reagents used in both cases.

Explanation

Both elimination (especially `beta`-elimination) and nuclephilic substitution reactions occurs simultaneously and compete with each other. However, one reaction can be made to be predominated over the other by a proper choice of reagents and reaction conditions. Thus the use of strong and bulkier bases and high temperature favour elimination reactions, whereas weaker and smaller bases and lower temperature favour substitution reactions.
`underset(19%)(CH_(3)-underset(OC_(2)H_5)underset(|)overset(CH_3)overset(|)(C)underset(25^(@)C)overset(C_(2)H_(5)OH)(larr)CH_(3)-underset(Br)underset(|)overset(CH_3)overset(|)(C)-CH_(3)underset("in"C_(2)H_(5)OH,Delta)overset(2(M)C_(2)H_(5)O^(Theta))(rarr)CH_(3)-underset(93%)overset(CH_3)overset(|)(C)=CH_(2)`.