It takes sally 4 hours to deliver newspapers. if kathy works alone, it takes her 6 hours. how long would it take them working together to deliver all of the newspapers?

Sally's rate is 1/4 job per hour. 
Kathy's rate is 1/6 job per hour. 

Can you solve the rest? Scroll down if you can't!

1/4 + 1/6 
= 3/12 + 2/12 
= 5/12
5/12 x 6 = 30/60.

It will take them half an hour combined. 

The answer is part a: use

5/8 beds for each square yard