Answer: The correct option is (b) 
Step-by-step explanation: Given that Abigail and Bailey wash dogs to make extra money. Abigail can wash all of the dogs in 5 hours and Bailey can wash all the dogs in 3 hours.
We are to find the time taken by them if they wash the dogs together.
Abigail can wash the dogs in 5 hours.
So, in 1 hour, the fraction of the dogs Abigail can wash is given by

Bailey can wash the dogs in 3 hours.
So, in 1 hour, the fraction of the dogs Bailey can wash is given by

Hence, if they work together, then the fraction of the dogs that they wash in 1 hour is given by

Therefore, the time taken by them to wash the dogs if they work together will be

Thus, option (b) is correct.