If the time taken by A is 9 hours more than time taken by A + B together and B takes 36 hours more than the time taken by A + B together, find the time taken by B to finish the work.

45

Let A + B takes x hours to complete the work

then A takes x + 9 hours

and B takes x + 36 hours

by the formula x= geometric mean of 9 and 36 i.e.  x²  = 9 × 36 

 x = 18

Then A takes 9 + 18= 27 hours

and B takes 9 + 36 = 45 hours