Question 889078
What Happened:  120 men worked at each individual rate of r km per day for 50 days, finishing 1.2 km of railway.
{{{RT=J}}}
{{{120*r*50=1.2}}} and notice this is not in units of "JOBS" but only in units of kilometers of rail track on the right, and kilometers per day and number of days on the left member.  The value for r can be found.


{{{r=1.2/(120*50)}}}
{{{r=1/(100*50)}}}
{{{highlight(r=1/5000)}}} kilometer/day for 1 man


Let n = how many additional men to add so that the remaining assigned unfinished railway can be done in the remaining expected days.


{{{(n+120)*r*(210-50)=6-1.2}}}
{{{highlight((n+120)(1/5000)(210-50)=6-1.2)}}}
I left this unfinished so you see what is happening with the numbers.  Solve for n.