Question 884801
Either situation is for 1 job.
r = the rate for one man.
{{{28r*21=1}}}  and for some unknown number m of additional men, {{{(28+m)r*14=1}}}.  These both are for 1 job and the two left members are equal.


{{{28r*21=(28+m)r*14}}}
{{{(1/14r)(28*21r)=(1/14r)(28+m)14r}}}
{{{42=28+m}}}
{{{m=42-28}}}
{{{highlight(m=14)}}}
Fourteen more men.