Can you help me with this problem!
Alex can pour concrete on a walkway in x hours alone while Andy can pour concrete on the same walkway in two more hours than Alex.
a. How fast can they pour concrete on the walkway if they work together?
b. If Emman can pour concrete on the same walkway in one more hour than Alex, and Roger can pour the same walkway in one hour less than Andy, who must work together to finish the job with the least time?