Given:
a.) Amy can clean the house in 7 hours.
b.) When she works together with Tom, the job takes 5 hours.
Let,
T = no. of hours Tom can clean the house
In this type of problem, we will be using the following formula:

Where,
1/t1 = time taken by first person
1/t2 = time taken by second person
1/tb = time taken if both do the work together
We get,








Therefore, Tom could finish cleaning the house in 17.5 Hours
The answer is 17.5 Hours