Answer:
Step-by-step explanation:
Answer is in below attachment
Answer:
Infinitely Many Solutions
Step-by-step explanation:

Answer:
15 and 5 hours.
Step-by-step explanation:
Call x the time taken by the first chap, and y the second.

Let's divide by 5 and play with the LHS of the first equation a bit:
we know how much x+y is ( first equation!) let's solve.
At this point it's easy to check that 
Too many questions to be typed out ... I did it on the paper instead.