<PRE><B>Question 1010694</B>
Call the time it takes Frank, f.  Then John takes f+9.  The normal setup looks like this:
t/A + t/B = 1
Now plug in and get
20/f + 20/(f+9) = 1
Multiply by f(f+9) and get
20(f+9) + 20f = f(f+9)
20f + 180 + 20f = f^2 + 9f
Now collect like terms and solve...we get
f^2 - 31f - 180 = 0
(f - 36)(f + 5) = 0
f = 36 hours
f+9 = 45 hours</PRE>