At x=a, limit is of 00 form.
So, applying L'Hospital rule, we get
x→alim(3a+x)31−(4x)31(a+2x)31−(3x)31=x→alim31(3a+x)−32.−31.(4x)−32.431(a+2x)−32.2−31.(3x)−32.3
=31(4a)−32.(1−4)31(3a)−32.(2−3)=4−323−32.31
=931234.31=(32)(92)31