Answer:
Step-by-step explanation:
Work finished by Francesca  in one hour = 1/6
Work finished by Irvin in one hour = 1/4
Work finished by Francesca and Irvin in one hour = 1/6 +1/4
                               [tex]=\frac{4}{24}+\frac{6}{24}\\\\=\frac{10}{24}\\\\=\frac{5}{12}\\[/tex]
5/12 of the work is completed by both in an hour
Whole work will be completed in 1*12/5 =12/5 hours = 2 2/5 hours
                         = 2 hours 24 minutes
