BA LLB Banaras Hindu University 2016 Solved Paper

LCM of $12,18,21,28$
$=2\times 2\times 3\times 3\times 7=252$Multiple of 252 is the answer
Let the 4 -digit greatest number be 9999
252)9999(39
  756
 ──────
  2439
  2268
 ──────
   171
Subtract 171 from 9999 .
This is the answer $=9999-171=9828$