Question 747578
Starting out we only know that their sum is 6 (so we cannot assume they are integers or consecutive, etc).

{{{j+k+l=6}}}


New numbers are
{{{(j+20)*10=10j+200}}}
{{{(k+20)*10=10k+200}}}
{{{(l+20)*10=10l+200}}}


New sum:


{{{
(10j+200)+(10k+200)+(10l+200)=10(j+k+l)+600=10(6)+600=660
}}}


:)