Question 1024218
This is ambiguous.  I will take as t days with 10 workers, and 35-t days with the remaining 5 workers.  This makes for a total job time of 35 days from start to finish.


{{{FullCrewWork+fiveCrewWork=1}}}, accounts for "one whole work".


Look at first sentence.
Let r be rate for one worker, jobs per days.
{{{10*r*20=1}}}
{{{highlight_green(r=1/20)}}}.



Use the needed data in the work-rates rule.
{{{10(1/20)*t+5(1/20)*(35-t)=1}}}
If this makes sense, and especially if you can formulate the equation on your own, then enough help done; just solve for t.