Working together, it takes sam, jenna, and francisco two hours to paint one room. when sam works alone, he can paint one room in 6 hours. when jenna works alone, she can paint one room in 4 hours. determine how long it would take francisco to paint one room on his own.

 12 hours

Step-by-step explanation:

Given : Working together, it takes Sam, Jenna, and Francisco two hours to paint one room.

When Sam works alone, he can paint one room in 6 hours. When Jenna works alone, she can paint one room in 4 hours.

Let 't' be the time taken by Francisco to paint one room on his own.

Then , we have

Rate of work of  Sam +Rate of work of Jenna + Rate of work of  Francisco =Rate of work they all do together

i.e.  

i.e.  

i.e.  

i.e.  

i.e.  

i.e.  

i.e. t= 12

Hence,  Francisco would take 12 hours to  paint one room on his own.

Total no. of students - 140 students
Total no. of students from all schools= 140+70+35+105=350
school A= 140÷350×100=40./. (multiplying by 100 because it's the total percentage )
School B = 70÷350×100=20./.
School C = 105÷350×100=30./.
School D = 105÷350×100= 10./.
Consisting all the schools percentage it gives 100./.

Hope this helps