correct entry that should have been recorded--
sales return A/c Dr. 5650
To X's A/c 5650
BUT entry posted in return inward is 90rs short and posting in X's A/c is 900 rs more.. so in order to reach the correct level of entry we will debit sales return A/c by rs 90 and debit excees of 900rs in X's A/c.
Hence the composite rectified entry will be sales return A/c Dr. 90
X's A/c Dr. 900
To suspense A/c 990
Credit to suspense A/c is done to reverse the effect of differnce which was coming in trial balance due to wrong posting of entries. TB showed some diff. which was put to suspense A/c. Now wen the error is detected and rectified ,suspense A/c will not appear on account of passing rectiffied entry.