Answer:
10 hours
Step-by-step explanation:
Since Eva works 4 times as fast as London, she is doing work equivalent to the work done by 4 Londons. Then all of the work is being done at a rate equivalent to having 5 Londons on the job.
If it takes 5 Londons 2 hours, then it would take one of them 5 times as long, 10 hours.
London working alone takes 10 hours to do the job.
