Given Relation:
R = {A, B, C, D, E}
Given Functional Dependencies:
AB → C
A → D
D → E
AC → B
Closure of AB
{AB}+ = {AB} (axiom of reflexivity)
= {ABC} (by union rule & given FD: AB → C)
= {ABCD} (by union rule & given FD: A → D)
= {ABCDE} (by union rule & given FD: D → E)
Closure of DC
{DC}+ = {DC} (axiom of reflexivity)
= {DCE} (by union rule & given FD: D → E)
Hence,
Closure of AB, {AB}+ = {ABCDE}
and
Closure of DC, {DC}+ = {CDE}