Question 1139732
{{{1/6+1/d=1/3}}}


{{{1/d=1/3-1/6}}}

{{{1/d=2/6-1/6=1/6}}}

{{{d=6}}}

Also notice the amounts of time given.  The two brothers together take half the time as either working alone.  Both each work at one job in 6 hours.