1/18 + 1/24 = 7/72
72/7 = 72/7 *2 = 20 4/7 days
A can do a job in 18 days and B can do it in 24 days. A and B working together will finish twice the amount of work in days?
Options:
  - 22 1/6
  - 22 1/2
  - 20 4/7
  - 22 1/9
  - 22 1/1