So, let's find the rates:
5 years = 1180 people
5n = 1180
n = 236
236*2 = 472
5600 + 472 = 6072
6072 people
I believe that the answer is 20.45
The amount of work done by Kalon in an hour is equal to 1/4. This is based on his time to finish the job. Letting x be the number of hours Marna can finish the job alone will let her finish 1/x of the job in an hour. If their rates are added together and multiplied by the number of hours they worked together, the product should be one whole job.
(1/4 + 1/x)(1 5/7) = 1
The value of x is 3. Therefore, it will take 3 hours for Marna to clean the chimney alone.
