hello aspirant,

the answers to your problems are as follows-

(i) (−3,0)={x:x belongs to R,−3<x<0}

(ii) [-6,12]={x:x belongs to R,-6≤x≤12}
(iii) [100,200]={x:x belongs to R,100≤x≤200}

(iv) (2,a)={x:x belongs to R,2<x<a} ; a is any positive integer greater than 2

(v) (−a,3)={x:x belongs to R,−a<x<3}  ; a is any negative integer smaller than -3

hope that helps

All the best