Answer:
5.1 hours
Explanation:
Given that :
Naomi:
Time taken = 9hours
Rate = 1/9
Ramona :
Time taken = 12 hours
Rate = 1/12
Working together :
Time. Taken = 1 / (sum of their rates)
Time taken = 1 / (1/9 + 1/12)
L. C. M of 9 and 12 = 36
Sum up f their rates :
(4 + 3) / 36 = 7/36
Time taken = 1 / (7/36)
= 36 / 7
= 5.142 = 5.1 hours