the first reaction is an elimination reaction that takes place in an alcoholic media
the second reaction is a substitution reaction that takes place in aqueous media
the answer depends on the medium of solvent

generally water favours subs and alcohol favours elimination

as in both reactions OH- is the base cum nucleophile

in alcohol R is a +I group so electrons are slightly displaced towards OH-

so OH- gets a strong -ve charge and hence can act as a base

which is not in the case of water